Master cylinder device and hydraulic brake system using the same

ABSTRACT

A master cylinder device includes a housing whose front side end is closed and which includes a third housing member separating an interior of the housing into a front side chamber and a rear side chamber and having an opening through the third housing member, a first pressurizing piston which includes a main body portion disposed in the front side chamber and which is moved forward by receiving a force for pressurizing the brake fluid to be supplied to a brake devices, and an input piston. In the master cylinder device, an input chamber into which a brake fluid is introduced is defined between a rear end of the main body portion of the first pressurizing piston and the third housing member. The input piston is fitted in the housing with seals, whereby, an inter-piston chamber across which the input piston and the pressure receiving piston face to each other.

This is a Continuation of application Ser. No. 13/993,090 filed Jun. 11,2013, which in turn is a National Stage Application of PCT/JP2011/054326filed Feb. 25, 2011. The disclosure of the prior applications is herebyincorporated by reference herein in its entirety.

TECHNICAL FIELD

This invention relates to a master cylinder device for pressurizing abrake fluid and supplying the pressurized brake fluid to a brake deviceprovided in a wheel, and a hydraulic brake system using the mastercylinder device.

BACKGROUND ART

Some master cylinder devices, such as a master cylinder device disclosedin the following patent literature, can pressurize a brake fluiddepending on a pressure of a brake fluid introduced from a high pressuresource irrespective of an operation force for operating a brakeoperation member by a driver. This master cylinder device includes apressure receiving piston which moves forward by a pressure of a brakefluid in an input chamber, that is, a fluid chamber into which the brakefluid is introduced and which then pressurizes a brake fluid, and aninput piston which is fitted in the pressure receiving piston at a blindhole thereof being open rearward and which moves forward by a brakeoperation. Between a bottom portion of the blind hole and a front endface of the input piston, there is generally formed a fluid chamberfilled with a brake fluid (hereinafter, referred to as an “inter-pistonchamber”, where appropriate). Therefore, the pressure receiving pistonand the input piston can move independently from each other.

-   Patent Literature 1: JP-A-2010-929 (P. 20, FIG. 3)

DISCLOSURE OF THE INVENTION (A) Summary of the Invention

In the master cylinder device disclosed in the above patent literature,when the pressure receiving piston and the input piston move relative toeach other in the master cylinder device, a seal between the pistonsgenerates a friction force. Therefore, when the pressure receivingpiston is moved by the brake fluid of a high pressure, a force causing amovement of the input piston acts on the input piston due to thefriction force, whereby operational feeling in a brake operation isdeteriorated. In addition, the above seal defines the inter-pistonchamber and the input chamber. The pressure of the brake fluid in theinput chamber becomes considerably high when a hydraulic brake forcegenerated in the brake device is comparatively large. Therefore, ahigh-pressure seal is employed as the above seal. Commonly, thehigh-pressure seal generates the friction force to be comparativelylarge. Consequently, a problem of the above deterioration of operationalfeeling appears more significantly. In addition, as the friction forcebecomes large, a resistance upon a movement of the input piston by theoperation force becomes large. This also deteriorates operationalfeeling in a brake operation. In the master cylinder device, there areleft many rooms for improvements including an improvement for copingwith the deterioration of operational feeling. So, if any improvement iscarried out, it is possible to improve utility of the master cylinderdevice. The present invention is developed in the light of the currentsituation described above. It is therefore an object of the presentinvention to improve utility of a master cylinder device and a hydraulicbrake system using the device.

To solve the described object, a master cylinder device according to thepresent invention comprises a housing whose front side end is closed andwhich includes a partition portion separating an interior of the housinginto a front side chamber and a rear side chamber and having an openingthrough the partition portion, a pressure receiving piston whichincludes a main body portion disposed in the front side chamber andwhich is moved forward by receiving a force for pressurizing a brakefluid to be supplied to a brake device, and an input piston which canmove forward by an operation force applied to a brake operation member.In the master cylinder device, an input chamber into which a brake fluidfrom a high pressure source is introduced is defined between a rear endof the main body portion of the pressure receiving piston and thepartition portion of the housing. Additionally, the input piston isfitted in the housing with a seal, whereby, between the input piston andthe pressure receiving piston, there is defined an inter-piston chamberacross which the input piston and the pressure receiving piston face toeach other by utilizing the opening formed in the partition portionthough the input piston and the pressure receiving piston are not fittedto each other with any seal.

In the master cylinder device according to the present invention, theinput piston is not fitted to the pressure receiving piston with a seal.Consequently, when the pressure receiving piston moves, no force causingany movement of the input piston, that is, no force resulting from anyfriction force of any seal acts on the input piston. Therefore,operational feeling in a brake operation is improved. In addition, sincethe pressure of the brake fluid in the input chamber does not act on aseal between the input piston and the housing, the seal is not requiredto be a high-pressure seal. Consequently, it is possible to make afriction force resulting from the seal upon a movement of the inputpiston be comparatively small. Therefore, operational feeling in a brakeoperation is improved. Owing to these improvements, the master cylinderdevice according to the present invention and a hydraulic brake systemusing the device have excellent utility.

(B) Forms of Invention

There will be exemplified and described various forms according to aninvention which is considered claimable (hereinafter referred to as“claimable invention” where appropriate). Each of the forms according tothe invention is numbered like the appended claims and depends from theother form or forms, where appropriate. This is for easier understandingof the claimable invention, and it is to be understood that combinationsof constituent elements that constitute the invention are not limited tothose described in the following forms. That is, it is to be understoodthat the claimable invention shall be construed in the light of thefollowing descriptions of various forms and preferred embodiments. It isto be further understood that any form in which one or more elementsis/are added to or deleted from any one of the following forms may beconsidered one form of the claimable invention. Some of the formsaccording to the claimable invention correspond to claims.

Specifically, in the following forms, the form (1) from which featuresregarding a communication passage and pressurized areas of the pressurereceiving piston are excluded corresponds to claim 1, the form (2)corresponds to claim 2, the form (3) corresponds to claim 3, the form(4) corresponds to claim 4, the form (5) corresponds to claim 5, theform (6) corresponds to claim 6, the form (7) corresponds to claim 7,the form (9) corresponds to claim 8, the form (10) corresponds to claim9, the form (11) corresponds to claim 10, the form (12) corresponds toclaim 11, the form (13) corresponds to claim 12, and the form (15)corresponds to claim 13, respectively.

The master cylinder device according to the claimable invention, asdescribed herein, are generally categorized into three types, morespecifically, an “Input Piston Free Type Master Cylinder Device”, a“Master-Cut System Adoptable Type Master Cylinder Device”, and a“Pressure Receiving Piston Lock Type Master Cylinder Device”. Herein,forms according to the invention are described in detail for each typeas follows.

<<Input Piston Free Type Master Cylinder Device>>

(1) A master cylinder device for supplying a pressurized brake fluid toa brake device provided in a wheel, comprising:

a housing whose front side end is closed and which includes a partitionportion separating an interior of the housing into a front side chamberand a rear side chamber and having an opening through the partitionportion;

a pressure receiving piston which includes a main body portion having aflange on a rear end thereof and disposed in the front side chamber, andwhich is moved forward by receiving a force for pressurizing the brakefluid to be supplied to the brake device; and

an input piston which is disposed in the rear side chamber, which isconnected to a brake operation member disposed behind the housing, andwhich can move forward by an operation force applied to the brakeoperation member,

wherein the main body portion of the pressure receiving piston isfitted, at the flange and a portion in front of the flange, in thehousing with respective seals and the pressure receiving piston isfitted in the partition portion of the housing with a seal, whereby: apressurizing chamber in which the brake fluid to be supplied to thebrake device is pressurized by a forward movement of the pressurereceiving piston is defined in front of the main body portion of thepressure receiving piston; an input chamber into which a brake fluidfrom a high pressure source is introduced is defined between a rear endof the main body portion and the partition portion; and an opposingchamber which opposes the input chamber with the flange being interposedbetween the opposing chamber and the input chamber is defined around themain body portion,

wherein the input piston is fitted in the housing with a seal, whereby,between the input piston and the pressure receiving piston, there isdefined an inter-piston chamber across which the input piston and thepressure receiving piston face to each other by utilizing the openingformed in the partition portion though the input piston and the pressurereceiving piston are not fitted to each other with any seal,

wherein an inter-chamber communication passage which allows acommunication between the opposing chamber and the inter-piston chamberis provided, and a pressurized area of the pressure receiving piston onwhich a pressure of a brake fluid in the opposing chamber acts and apressurized area of the pressure receiving piston on which a pressure ofa brake fluid in the inter-piston chamber acts are equal, and

wherein the master cylinder device further comprises a reaction forceapplying mechanism which allows a forward movement of the input pistonrelative to the housing by the operation force, and which applies, tothe input piston, a reaction force against the forward movement and witha magnitude according to an amount of the forward movement, as anoperation reaction force against an operation of the brake operationmember.

According to the master cylinder device of this form, when a driveroperates the brake operation member, the driver can feel the operationreaction force by the reaction force applying mechanism while the inputpiston moves forward. On the other hand, when the brake fluid isintroduced from the high pressure source to the input chamber, thepressure receiving piston moves forward, thereby pressurizing the brakefluid in the pressurizing chamber so as to supply the pressurized brakefluid to the brake device. Such movements of the input piston and thepressure receiving piston change respective volumes of the inter-pistonchamber and the opposing chamber inside the master cylinder device. Onthe volume changes, according to the master cylinder device, since theinter-piston chamber and the opposing chamber communicate with eachother through the inter-chamber communication passage, a pressure of thebrake fluid in the inter-piston chamber and a pressure of the brakefluid in the opposing chamber become equal. Moreover, since thepressurized area of the pressure receiving piston on which the brakefluid in the opposing chamber acts and the pressurized area of thepressure receiving piston on which the brake fluid in the inter-pistonchamber acts are equal, a forward bias force acting on the pressurereceiving piston by the pressure of the brake fluid in the inter-pistonchamber and a rearward bias force acting on the pressure receivingpiston by the pressure of the brake fluid in the opposing chamber becomeequal. In other words, the master cylinder device is configured suchthat, for example, even when the input piston is moved by a brakeoperation and thus the pressure of the brake fluid in the inter-pistonchamber is changed, this pressure change does not cause any movement ofthe pressure receiving piston. From another point of view, the mastercylinder device is configured such that, when the pressure receivingpiston is moved, a volume decrease amount of one of the opposing and theinter-piston chambers and a volume increase amount of the other of thembecome equal, in other words, a decrease amount of the brake fluid inone of them and an increase amount of the brake fluid in the other ofthem become equal. Accordingly, when the pressure receiving pistonmoves, a volume of each of the opposing chamber and the inter-pistonchamber changes while the brake fluid flows between the chambers.Therefore, the master cylinder device is configured such that, forexample, even when the pressure receiving piston is moved by the brakefluid introduced from the high pressure source, this movement does notcause any movement of the input piston. That is, the master cylinderdevice is configured such that the pressure receiving piston and theinput piston can move independently from each other. Consequently, themaster cylinder device can realize a “high-pressure-source-pressuredependent pressurizing state”, that is, a state in which the brake fluidto be supplied to the brake device is pressurized depending on not theoperation force for operating the brake operation member but only apressure of the brake fluid introduced from the high pressure source.This pressure is hereinafter referred to as a “high-pressure-sourcepressure”, where appropriate. So to say, the master cylinder device canrealize the high-pressure-source-pressure dependent pressurizing statewith the input piston being able to move freely relative to the pressurereceiving piston, therefore the master cylinder device is called an“Input Piston Free Type Master Cylinder Device”.

In addition, where the operation force is transmitted to the pressurereceiving piston in a realization of the high-pressure-source-pressuredependent pressurizing state, the master cylinder device can realize an“operation-force/high-pressure-source-pressure dependent pressurizingstate”, that is, a state in which the brake fluid to be supplied to thebrake device is pressurized depending on not only thehigh-pressure-source pressure but also the operation force. In thisstate, the brake device can generate a hydraulic brake force with amagnitude dependent on the high-pressure-source pressure plus ahydraulic brake force with a magnitude dependent on the operation force.In order to transmit the operation force to the pressure receivingpiston, for example, the input piston may be allowed to come into anabutting contact with the pressure receiving piston, or alternatively,the inter-piston chamber may be hermetically closed. More specifically,where the input piston is allowed to come into an abutting contact withthe pressure receiving piston, the operation force is transmitted, owingto the abutting contact, from the input piston to the pressure receivingpiston. On the other hand, where the inter-piston chamber ishermetically closed, the operation force is transmitted, via the brakefluid in the inter-piston chamber, to the pressure receiving piston.

When the operation-force/high-pressure-source-pressure dependentpressurizing state is realized, the brake device can be actuateddepending on not only the high-pressure-source pressure but also theoperation force. Thus, the hydraulic brake force generated by the brakedevice can be comparatively large. Therefore, where theoperation-force/high-pressure-source-pressure dependent pressurizingstate is realized in a condition in which a large hydraulic brake forceis required, such as a condition of an emergency brake, the brake devicecan generate a large hydraulic brake force. In order to determinewhether the large hydraulic brake force is required or not, for example,the master cylinder device may include a sensor for detecting thehydraulic brake force and a controller for executing the determinationbased on a detected value of the sensor. The sensor for detecting thehydraulic brake force may be, for example, a sensor for detecting apressure of the brake fluid in the pressurizing chamber, a pressure ofthe brake fluid in the input chamber, the brake operation force, or thelike.

By the way, in order to generate a large hydraulic brake force dependingon only the high-pressure-source pressure, the pressure of the brakefluid introduced into the input chamber must be intensified considerablyhigh. Therefore, the high pressure source having a comparatively largeoutput capability, such as a large hydraulic pump, is necessary. Thatcauses an increase of a mounting space for the master cylinder device,and an increase of cost as well. Since the master cylinder device mayrealize the operation-force/high-pressure-source-pressure dependentpressurizing state, a large hydraulic brake force can be generated byusing the high pressure source having a comparatively small outputcapability.

In addition, even when the brake fluid is not introduced from the highpressure source, as in the operation-force/high-pressure-source-pressuredependent pressurizing state, an allowance of the input piston to comeinto an abutting contact with the pressure receiving piston, oralternatively, a hermetical closing of the inter-piston chamber canrealize an “operation-force dependent pressurizing state”, that is, astate in which the brake fluid supplied to the brake device ispressurized depending on only the operation force. Therefore, forexample, even in a condition in which the high pressure source cannotwork due to an electric failure etc., the brake device can be actuateddepending on the operation force.

In the master cylinder device of this form, the input piston and thepressure receiving piston are not fitted to each other with any seal.Therefore, a movement of the pressure receiving piston by anintroduction of the brake fluid from the high pressure source to theinput chamber causes no friction force resulting from any seal togenerate between the pressure receiving piston and the input piston.Accordingly, a movement of the pressure receiving piston causes no forcecausing any movement of the input piston, that is, no force resultingfrom any friction force of any seal to act on the input piston. In otherwords, a movement of the pressure receiving piston does not pull theinput piston and the operation member. Therefore, operational feeling ina brake operation is excellent.

In the master cylinder device of this form, the pressure receivingpiston is fitted, at the flange formed in the rear end of the main bodyportion, in the housing with the seal, and is fitted in the partitionportion of the housing with the seal, whereby the input chamber isdefined. For example, in the high-pressure-source-pressure dependentpressurizing state and the operation-force/high-pressure-source-pressuredependent pressurizing state, the brake fluid in the input chamber mayhave a considerably high pressure. Therefore, high-pressure seals areemployed as the seals between the pressure receiving piston and thehousing, each of which generates a comparatively large friction forcewhen the pressure receiving piston is moved. On the other hand, in themaster cylinder device of this form, since the pressure of the brakefluid in the input chamber does not act on the seal between the inputpiston and the housing, the seal is not required to be a high-pressureseal. Consequently, it is possible to make a friction force resultingfrom the seal upon a movement of the input piston be comparativelysmall. That is, a resistance upon a movement of the input piston iscomparatively small, whereby operational feeling in a brake operation isexcellent. Especially in the operation-force dependent pressurizingstate, it is possible to provide excellent operational feeling.

It is noted that, in the master cylinder device herein, the “forwardmovement of the input piston” means not only a movement of a whole ofthe input piston but also a movement of a part of the input piston. Forexample, in the input piston capable of shrinking as described later, aforward movement of a part of the input piston to which the brakeoperation member is connected is considered the forward movement of theinput piston in the master cylinder device of this form.

Additionally, in the master cylinder device, for example, when thehigh-pressure-source-pressure dependent pressurizing state is realized,a force by the pressure of the brake fluid in the pressurizing chamberis not transmitted to the brake operation member. However, in the mastercylinder device of this form, owing to the reaction force applyingmechanism, the operation reaction force is applied to the input pistonwhile the forward movement of the input piston is allowed. Therefore, adriver can feel like pressurizing the brake fluid in the pressurizingchamber by the driver's operation force, that is, operating the brakedevice. That is, in the master cylinder device of this form, a so-calledstroke simulator is constituted by the reaction force applyingmechanism.

(2) The master cylinder device according to the form (1),

wherein the pressure receiving piston includes an extension portionextending from the main body portion through the opening of thepartition portion into the rear side chamber, and is fitted, at theextension portion, in the partition portion with the seal, whereby theinput chamber is defined, and the inter-piston chamber is defined suchthat a rear end of the extension portion and the input piston face toeach other.

In the master cylinder device of this form, the input chamber is definedto have an annular shape in a space around the extension portion. Also,since the extension portion extends beyond the partition portion intothe rear side chamber, the inter-piston chamber is defined including aspace across which a rear end face of the extension portion and a frontend face of the input piston face to each other.

(3) The master cylinder device according to the form (2),

wherein one of a front side portion of the input piston and a rear sideportion of the extension portion of the pressure receiving piston isformed into a hollow cylindrical shape, and the other of them isinserted in the one of them.

In the master cylinder device of this form, one of a rear side part ofthe pressure receiving piston and a front side part of the input pistonis located inside the other of them. Since the pressure receiving pistonand the input piston are arranged thus, a part of the pressure receivingpiston and a part of the input piston overlap with each other in afront-back direction, whereby the total length of the master cylinderdevice can be shortened while respective necessary lengths of thosepistons are secured. In the master cylinder device of this form, even ineither a construction in which the front side portion of the inputpiston is formed into a hollow cylindrical shape or a construction inwhich the rear side portion of the extension portion of the pressurereceiving piston is formed into a hollow cylindrical shape, theinter-piston chamber is defined including a space present inside theportion having the hollow cylindrical shape.

(4) The master cylinder device according to the form (1),

wherein the partition portion of the housing includes an annularseparation wall portion projecting to inside the housing in a radialdirection and an inner cylindrical portion having a hollow cylindricalshape and extending forward from an inner periphery of the separationwall portion, a front end of the inner cylindrical portion functions asthe opening, and an interior of the inner cylindrical portion serves asa part of the rear side chamber,

wherein the main body portion of the pressure receiving piston includesa blind hole which is open rearward, whereby a rear side portion of themain body portion is a cylindrical portion having a hollow cylindricalshape, and the main body portion has the flange at a rear end of thecylindrical portion,

wherein the pressure receiving piston is disposed such that the innercylindrical portion of the partition portion is inserted in thecylindrical portion of the pressure receiving piston, and the pressurereceiving piston and the partition portion are fitted at an innercircumferential face of the cylindrical portion and an outercircumferential face of the inner cylindrical portion to each other withthe seal, whereby the input chamber is defined between a rear end of thecylindrical portion and the separation wall portion of the partitionportion, and

wherein the inter-piston chamber is defined such that a bottom portionof the blind hole of the pressure receiving piston and the input pistonface to each other with the opening formed in the partition portionbeing interposed between the bottom portion and the input piston.

In the master cylinder device of this form, the housing can beconsidered to have a double-cylindrical structure. That is, the housinghas a portion outside the inner cylindrical portion which can be calledan outer cylindrical portion, therefore the cylindrical portion of thepressure receiving piston can be considered to be interposed between theinner cylindrical portion and the outer cylindrical portion. Inaddition, the input chamber can be considered to be a fluid chambersurrounded at a rear end of the cylindrical portion by the flange, theouter cylindrical portion, the separation wall portion, and the innercylindrical portion.

(5) The master cylinder device according to the form (4),

wherein the input piston is disposed such that at least a part of theinput piston including a front end thereof is inserted in the innercylindrical portion.

In the master cylinder device of this form, a part of the input pistoncan be positioned in the cylindrical portion of the pressure receivingpiston. Therefore, a part of the pressure receiving piston and a part ofthe input piston overlap with each other in the front-back direction,whereby the total length of the master cylinder device can be shortenedwhile respective necessary lengths of those pistons are secured. Inaddition, in the master cylinder device of this form, the inter-pistonchamber is defined including a space across which a bottom face of thecylindrical portion and the front end face of the input piston face toeach other.

(6) The master cylinder device according to the form (5),

wherein the input piston is fitted, at the at least a part of the inputpiston, in the inner cylindrical portion with a seal.

In the master cylinder device of this form, since the input piston isfitted, at a part inserted in the inner cylindrical portion, in thehousing with a seal, the inter-piston chamber is defined in the innercylindrical portion.

(7) The master cylinder device according to any one of the forms(1)-(6),

wherein the reaction force applying mechanism includes a fluid storagechamber communicating with the opposing chamber and the inter-pistonchamber, and an elastic-reaction-force applying mechanism for the fluidstorage chamber which allows an increase of a volume of the fluidstorage chamber according to a decrease of a total volume of theopposing chamber and the inter-piston chamber, and which applies anelastic reaction force with a magnitude according to an amount of theincrease of the volume to a brake fluid in the fluid storage chamber.

In the master cylinder device of this form, the elastic reaction forceby the elastic-reaction-force applying mechanism for the fluid storagechamber also acts on the brake fluid in each of the opposing chamber andthe inter-piston chamber so as to change the pressure of the brake fluidin each of those chambers. More specifically, when the input pistonmoves forward, that is, a brake operation amount increases, the totalvolume of the opposing chamber and the inter-piston chamber decreases,and the volume of the fluid storage chamber increases by a volume of thebrake fluids decreased in the above chambers, whereby the elasticreaction force increases. Consequently, the pressure of the brake fluidin each of the opposing chamber and the inter-piston chamber increases,whereby a bias force acting on the input piston to move the input pistonrearward increases. Therefore, a driver can feel the increase of thebias force as an increase of the operation reaction force against theincrease of the brake operation amount by the driver.

(8) The master cylinder device according to the form (7),

wherein the reaction force applying mechanism includes a reaction forceapplying device disposed outside the housing and having the fluidstorage chamber and the elastic-reaction-force applying mechanism forthe fluid storage chamber.

In the master cylinder device of this form, at least a part of thereaction force applying mechanism, in other words, a main part of thestroke simulator is provided outside the housing, whereby a structureinside the housing can be made comparatively simple.

(9) The master cylinder device according to any one of the forms(1)-(8),

wherein the reaction force applying mechanism includes anelastic-reaction-force applying mechanism for the input piston whichallows a front end portion of the input piston defining the inter-pistonchamber to recede relative to another portion connected to the brakeoperation member, thereby allowing the input piston to shrink, and whichapplies an elastic reaction force with a magnitude according to anamount of the shrink of the input piston.

In the master cylinder device of this form, a movement of the inputpiston relative to the pressure receiving piston is allowed by theshrink of the input piston. More specifically, even when the totalvolume of the opposing chamber and the inter-piston chamber is fixed,the forward movement of the input piston relative to the pressurereceiving piston is allowed by that another portion of the input pistonmoves forward relative to the front end portion. Additionally, in theshrink of the input piston, a rearward bias force by theelastic-reaction-force applying mechanism for the input piston acts onanother portion connected to the brake operation member. Therefore, adriver can feel the bias force as the operation reaction force against abrake operation by the driver. By the way, the reaction force applyingmechanism of the master cylinder device may have twoelastic-reaction-force-applying mechanisms, that is, theelastic-reaction-force applying mechanism for the input piston and theelastic-reaction-force applying mechanism for the fluid storage chamber.

(10) The master cylinder device according to any one of the forms(1)-(9),

wherein a front end portion of the input piston defining theinter-piston chamber is allowed to recede relative to another portionconnected to the brake operation member, whereby the input piston isallowed to shrink, and

wherein the master cylinder device further comprises aninput-piston-shrink prohibiting mechanism which prohibits the shrink ofthe input piston.

For example, in the master cylinder device equipped with theelastic-reaction-force applying mechanism for the input piston, when theshrink of the input piston is allowed, the operation force istransmitted to the pressure receiving piston while shrinking the inputpiston. However, the shrink of the input piston would cause the brakeoperation amount to ineffectively become large. The master cylinderdevice of this form may prohibit the shrink of the input piston, whenpressurizing the brake fluid depending on the operation force, so as totransmit the operation force to the pressure receiving piston withoutgenerating an ineffective brake operation amount. This feature isadvantageous in the operation-force dependent pressurizing state inparticular.

(11) The master cylinder device according to any one of the forms(1)-(10),

wherein the master cylinder device comprises a low-pressure-sourcecommunication mechanism for the opposing and inter-piston chambers whichallows the opposing chamber and the inter-piston chamber to communicatewith a low pressure source.

In the master cylinder device of this form, when the low-pressure-sourcecommunication mechanism for the opposing and inter-piston chambersfunctions, the input piston can move forward relative to the pressurereceiving piston with the brake fluids in the opposing and inter-pistonchambers being flowed into the low pressure source. Therefore, the inputpiston can come into an abutting contact with the pressure receivingpiston, thereby transmitting the operation force to the pressurereceiving piston. That is, since it is possible to move the pressurereceiving piston forward depending on the operation force, thelow-pressure-source communication mechanism for the opposing andinter-piston chambers can be considered a mechanism for realizing theoperation-force dependent pressurizing state and theoperation-force/high-pressure-source-pressure dependent pressurizingstate. It is noted that, even where the master cylinder device includesthe elastic-reaction-force applying mechanism for the fluid storagechamber or the elastic-reaction-force applying mechanism for the inputpiston, the operation reaction force by the elastic-reaction-forceapplying mechanism does not generate when the opposing chamber and theinter-piston chamber communicate with the low pressure source by thelow-pressure-source communication mechanism for the opposing andinter-piston chambers. Consequently, the input piston can easily comeinto an abutting contact with the pressure receiving piston by theoperation force.

For example, a mechanism having a normally-opened electromagnetic valveas a main component may be employed as the low-pressure-sourcecommunication mechanism for the opposing and inter-piston chambers. Thatis, in a case in which the master cylinder device is configured to makethe opposing chamber and the inter-piston chamber communicate with thelow pressure source by opening an electromagnetic valve, anormally-opened valve opens simultaneously at a moment when an electricfailure occurs, and then the opposing chamber and the inter-pistonchamber communicate with the low pressure source. In other words, such alow-pressure-source communication mechanism for the opposing andinter-piston chambers can allow the master cylinder device to beautomatically actuated in the operation-force dependent pressurizingstate in an electric failure condition.

(12) The master cylinder device according to any one of the forms(1)-(10),

wherein the master cylinder device comprises a low-pressure-sourcecommunication mechanism for the opposing chamber which allows theopposing chamber to communicate with a low pressure source, and aninter-piston-chamber hermetically closing mechanism which hermeticallycloses the inter-piston chamber by shutting off the inter-chambercommunication passage.

In the master cylinder device of this form, when theinter-piston-chamber hermetically closing mechanism functions, theoperation force can be transmitted to the pressure receiving piston viathe brake fluid in the inter-piston chamber. Accordingly, in a case inwhich the forward movement of the pressure receiving piston is allowed,it is possible to move the pressure receiving piston forward dependingon the operation force. Therefore, the inter-piston-chamber hermeticallyclosing mechanism may be considered a mechanism for realizing theoperation-force dependent pressurizing state and theoperation-force/high-pressure-source-pressure dependent pressurizingstate. In addition, when the low-pressure-source communication mechanismfor the opposing chamber functions, the brake fluid in the opposingchamber never causes the rearward bias force to act on the pressurereceiving piston. That is, when the both mechanisms function, thepressure receiving piston can be moved forward while the rearward biasforce being a resistance force against the forward movement of thepressure receiving piston is not generated.

For example, a mechanism having a normally-closed electromagnetic valveas a main component may be employed as the inter-piston-chamberhermetically closing mechanism. That is, in case in which the mastercylinder device is configured to hermetically close the inter-pistonchamber by closing an electromagnetic valve, a normally-closed valvecloses simultaneously at a moment when an electric failure occurs, andthen the inter-piston chamber is hermetically closed. On the other hand,a mechanism having a normally-opened electromagnetic valve as a maincomponent may be employed as the low-pressure-source communicationmechanism for the opposing chamber. That is, in case in which the mastercylinder device is configured to make the opposing chamber communicatewith the low pressure source by opening an electromagnetic valve, anormally-opened valve opens simultaneously at a moment when an electricfailure occurs, and then the opposing chamber communicates with the lowpressure source. In other words, such an inter-piston-chamberhermetically closing mechanism and a low-pressure-source communicationmechanism for the opposing chamber can allow the master cylinder deviceto be automatically actuated in the operation-force dependentpressurizing state in an electric failure condition.

(13) A hydraulic brake system, comprising:

the master cylinder device according to any one of the forms (1)-(12);

a high pressure source device, as the high pressure source, whichintensifies a pressure of a brake fluid; and

a pressure adjusting device which adjusts a pressure of a brake fluid tobe introduced from the high pressure source device to the input chambersof the master cylinder device.

In the hydraulic brake system of this form, the brake fluid from thehigh pressure source device is introduced into the master cylinderdevice via the pressure adjusting device. Therefore, In thehigh-pressure-source-pressure dependent pressurizing state and theoperation-force/high-pressure-source-pressure dependent pressurizingstate, the pressure of the brake fluid is adjusted by the pressureadjusting device, whereby the pressure of the brake fluid in thepressurizing chamber can be adjusted to a pressure according to apressure of the pressure-adjusted brake fluid. In other words, thehydraulic brake force by the brake device can be adjusted.

The hydraulic brake system of this form is favorable for a brake systemprovided in a hybrid vehicle etc. That is, it is favorable for a vehiclehaving a brake system which is also capable of braking the vehicle byusing a regenerative brake force generated by an electric motor.Therefore, in a vehicle employing the system of this form, when anecessary brake force is small, the pressure of the brake fluid in thepressurizing chamber may be adjusted not to generate the hydraulic brakeforce and the vehicle may be braked depending on only the regenerativebrake force. When the necessary brake force is large, the pressure ofthe brake fluid in the pressurizing chamber may be adjusted to generatethe hydraulic brake force with a magnitude obtained by subtracting theregenerative brake force from the necessary brake force and the vehiclemay be braked depending on the regenerative brake force plus thehydraulic brake force.

In order to control an activation of the pressure adjusting device asdescribed above, the hydraulic brake system may have a sensor fordetecting the brake operation amount, and a controller for outputting acommand to the pressure adjusting device based on the detected value ofthe sensor. In addition, where the hydraulic brake system has a sensorfor detecting the adjusted pressure, a pressure detected by the sensoris fed back to the controller, and then the adjusted pressure may beconfirmed to have a degree according to the command.

(14) The hydraulic brake system according to the form (13),

wherein the high pressure source device includes a hydraulic pump whichintensifies the pressure of the brake fluid, and an accumulator whichstores the pressure-intensified brake fluid.

The high pressure source device of the hydraulic brake system of thisform may introduce the highly-pressurized brake fluid stored in theaccumulator into the input chamber. Accordingly, for example, where theaccumulator is configured to store a certain amount of the brake fluid,the hydraulic pump need not be worked at all times but may be workedonly in a time when a pressure of the brake fluid in the accumulator isbelow a predetermined pressure.

(15) The hydraulic brake system according to the form (13) or (14),

wherein the pressure adjusting device is configured to be controlled toreduce the pressure of the brake fluid supplied from the high pressuresource device to a pressure according to the control, and configured tosupply the pressure-reduced brake fluid to the master cylinder device,and

wherein the pressure adjusting device includes apilot-pressure-dependent pressure reducing mechanism which utilizes, asa pilot pressure, any one of a pressure of the brake fluid in thepressurizing chamber, a pressure of the brake fluid in the opposingchamber, and a pressure of the brake fluid in the inter-piston chamber,and which reduces the pressure of the brake fluid supplied from the highpressure source device to a pressure according to the pilot pressure.

In order to reduce the pressure of the brake fluid, the pressureadjusting device of the hydraulic brake system of this form isconsidered, from a constitution described in the former part of thisform, to be provided with a pressure reducing mechanism, that is, amechanism for reducing the pressure of the brake fluid supplied from thehigh pressure source device. This pressure reducing mechanism may be,for example, a valve device etc. which can communicate with the lowpressure source and can electrically adjust a valve opening pressure.Such a valve device can adjust the valve opening pressure according tothe control, and may open at the valve opening pressure, therebyallowing the brake fluid from the high pressure source device to outflowto the low pressure source. That is, the pressure of the brake fluidfrom the high pressure source device can be reduced to a pressureaccording to the control. Where the valve device constitutes thepressure reducing mechanism, for example, the pressure reducingmechanism may be utilized as a main pressure reducing mechanism of thepressure adjusting device, and the pilot-pressure-dependent pressurereducing mechanism described in the latter part of this form may beutilized as an auxiliary pressure reducing mechanism. More specifically,for example, the pressure adjusting device may be configured such thatthe pilot-pressure-dependent pressure reducing mechanism can reduce thepressure of the brake fluid supplied from the high pressure sourcedevice in a condition in which the valve device cannot work due to afailure etc. Alternatively, the pressure adjusting device may beconfigured such that the pilot-pressure-dependent pressure reducingmechanism can reduce the pressure of the brake fluid supplied from thehigh pressure source device as long as the accumulator of the highpressure source device stores the highly-pressurized brake fluid even ina condition in which the whole of the brake system or the whole of thevehicle undergoes an electric failure.

By the way, the pilot-pressure-dependent pressure reducing mechanism mayuse, as a pilot pressure, not only a pressure of any one of thepressurizing chamber, the opposing chamber, and the inter-piston chamberbut also a pressure of another fluid chamber indicating the pressure ofany one of these chambers. For example, in a master cylinder device inwhich a fluid chamber is defined inside the input piston allowed toshrink and which includes an input-piston-shrink prohibiting mechanismprohibiting the shrink of the input piston by hermetically closing theinside fluid chamber, when a front end of the input piston comes into anabutting contact with the pressure receiving piston with the shrink ofthe input piston being prohibited, a force by the pressure of the brakefluid in the inside fluid chamber has a magnitude to be equal to a forceby the pressure of the brake fluid in the pressurizing chamber via thepressure receiving piston. Therefore, the pressure of the fluid chamberinside the input piston is a pressure indicative of the pressure of thepressurizing chamber and may be utilized as the pilot pressure.

(16) The hydraulic brake system according to the form (15),

wherein the pilot-pressure-dependent pressure reducing mechanism isconfigured to utilize the pressure of the brake fluid in thepressurizing chamber of the master cylinder device as the pilotpressure.

In the hydraulic brake system of this form, the pressure adjustingdevice can reduce, by the pilot-pressure-dependent pressure reducingmechanism, the pressure of the brake fluid supplied from the highpressure source device according to the pressure of the brake fluid inthe pressurizing chamber. That is, for example, even in a condition inwhich an electric failure etc. occurs, when the pressure of the brakefluid in the pressurizing chamber is changed by the operation force, thepressure adjusting device can be activated by utilizing the pressure asthe pilot pressure.

(17) The hydraulic brake system according to the form (15),

wherein the pilot-pressure-dependent pressure reducing mechanism isconfigured to utilize the pressure of the brake fluid in theinter-piston chamber of the master cylinder device as the pilotpressure.

The pilot-pressure-dependent pressure reducing mechanism of thehydraulic brake system of this form is favorable for the master cylinderdevice which is configured to hermetically close the inter-pistonchamber in a condition in which an electric failure etc. occurs. Thatis, in such a master cylinder device, the pressure of the brake fluid inthe inter-piston chamber changes according to a brake operation, and thepressure adjusting device can reduce the pressure of the brake fluidfrom the high pressure source device according to the change of thepressure of the inter-piston chamber. It is noted that, since thepressure change of the brake fluid in the inter-piston chamber is causedby a movement of the input piston, the pressure change can follow achange of a brake operation comparatively well. That is, in the abovedescribed hydraulic brake system utilizing the pressure of the brakefluid in the pressurizing chamber as the pilot pressure, a pressurechange of the brake fluid in the pressurizing chamber is affected by afriction force etc. upon a movement of the pressure receiving piston. Inthe hydraulic brake system of this form, since the pressure change ofthe brake fluid in the inter-piston chamber is not affected by thefriction force etc., it follows a change of a brake operationcomparatively well. Therefore, operational feeling in a brake operationis excellent when the pressure of the brake fluid from the high pressuresource device is reduced by the pilot-pressure-dependent pressurereducing mechanism.

<<Master-Cut System Adoptable Type Master Cylinder Device>>

(21) A master cylinder device for supplying a pressurized brake fluid toa brake device provided in a wheel, comprising:

a housing whose front side end is closed and which includes a partitionportion separating an interior of the housing into a front side chamberand a rear side chamber and having an opening through the partitionportion;

a pressure receiving piston which includes a main body portion disposedin the front side chamber, and which is moved forward by receiving aforce for pressurizing the brake fluid to be supplied to the brakedevice; and

an input piston which is disposed in the rear side chamber, which isconnected to a brake operation member disposed behind the housing, andwhich is moved forward by an operation force applied to the brakeoperation member,

wherein the pressure receiving piston is fitted, at the main bodyportion, in the housing with a seal and fitted in the partition portionwith a seal, whereby an input chamber into which a brake fluid from ahigh pressure source is introduced is defined between a rear end of themain body portion and the partition portion,

wherein the input piston is fitted in the housing with a seal, whereby,between the input piston and the pressure receiving piston, there isdefined an inter-piston chamber across which the input piston and thepressure receiving piston face to each other by utilizing the openingformed in the partition portion though the input piston and the pressurereceiving piston are not fitted to each other with any seal, and

wherein the master cylinder device further comprises a reaction forceapplying mechanism which is configured to allow a relative forwardmovement of the input piston relative to the pressure receiving pistonby the operation force in a state in which a decrease of a volume of theinter-piston chamber is allowed, and which is configured to apply to thepressure receiving piston and the input piston a reaction force againstthe relative forward movement and with a magnitude according to anamount of the relative forward movement such that the reaction forceacts as an operation reaction force against an operation of the brakeoperation member.

In the master cylinder device of this form, when a driver operates thebrake operation member and the input piston moves forward relative tothe pressure receiving piston, the driver can feel the reaction forceapplied to the input piston by the reaction force applying mechanism asthe operation reaction force. The reaction force by the reaction forceapplying mechanism also acts on the pressure receiving piston, and thusthe operation force is considered to be transmitted to the pressurereceiving piston. Consequently, the pressure receiving piston can bemoved forward by the operation force so as to pressurize the brake fluidto be supplied to the brake device. On the other hand, when the brakefluid from the high pressure source is introduced into the inputchamber, a pressure of the brake fluid causes a forward bias force toact on the pressure receiving piston. Therefore, the pressure receivingpiston can be moved forward by the bias force too. In other words, thepressure receiving piston can be also moved forward depending on thehigh-pressure-source pressure so as to pressurize the brake fluid to besupplied to the brake device. Consequently, in the master cylinderdevice of this form, the operation-force/high-pressure-source-pressuredependent pressurizing state is realized at all times.

In a case in which the supply of the pressurized brake fluid from thismaster cylinder device to the brake device is shut off, the brake deviceis never actuated by the supply of the brake fluid from the mastercylinder device. Even in this case, where a hydraulic brake systemequipped with the master cylinder device is configured to introduce,directly into the brake device, the brake fluid whose pressure isintensified by the high pressure source, the brake device can generatethe hydraulic brake force depending on the pressure of the brake fluid,namely, the high-pressure-source pressure. For example, where thehydraulic brake system which includes a communication passage forsupplying the brake fluid pressurized by the master cylinder device tothe brake device and in which an electromagnetic valve is provided inthe communication passage, it is possible to shut off the supply of thepressurized brake fluid from the master cylinder device to the brakedevice by closing the electromagnetic valve. In addition, where thehydraulic brake system includes a communication passage for supplyingthe brake fluid from the high pressure source to the brake device and anelectromagnetic valve provided in the communication passage, it ispossible to supply the pressurized brake fluid from the high pressuresource to the brake device by opening the electromagnetic valve.Accordingly, where, in a normal condition, the supply of the brake fluidfrom the master cylinder device to the brake device is shut off and thebrake fluid is supplied from the high pressure source to the brakedevice, a state in which the hydraulic brake force with a magnitudedependent on not the operation force for operating the brake operationmember but the high-pressure-source pressure is generated is realized inthe brake device. So to say, in the hydraulic brake system equipped withthe master cylinder device of this form, the brake fluid is suppliedfrom the high pressure source to the brake device and the communicationbetween the master cylinder device and the brake device is shut (cut)off, whereby a state is realized in which the hydraulic brake force witha magnitude dependent on only the high-pressure-source pressure isgenerated, therefore the master cylinder device is called a “Master-CutSystem Adoptable Type Master Cylinder Device”.

In addition, when the supply of the brake fluid from the high pressuresource to the brake device is shut off and the brake fluid is suppliedfrom the master cylinder device to the brake device, the forwardmovement of the pressure receiving piston is allowed. Therefore, thebrake device generates the hydraulic brake force by the supply of thebrake fluid from the master cylinder device. In this state, the brakedevice generates the hydraulic brake force with a magnitude according tothe pressure of the brake fluid pressurized in the master cylinderdevice depending on the operation force and the high-pressure-sourcepressure. Therefore, for example, where the supply of the brake fluidfrom the high pressure source to the brake device is shut off and thebrake fluid is supplied from the master cylinder device to the brakedevice in a condition in which a large hydraulic brake force isrequired, such as a condition of an emergency brake, the brake devicecan generate a comparatively large hydraulic brake force. In otherwords, the master cylinder device in which the“operation-force/high-pressure-source-pressure dependent pressurizingstate” is realized is made to communicate with the brake device, wherebythe brake device is put into a state in which the hydraulic brake forcewith a magnitude dependent on the high-pressure-source pressure plus thehydraulic brake force with a magnitude dependent on the operation forcegenerates.

It is desirable that a switch of a supply source of the brake fluid tothe brake device, that is, the switch of the supply of the brake fluidfrom the high pressure source to the brake device and the shut-off ofthe supply as well as the switch of the supply of the brake fluid fromthe master cylinder device to the brake device and the shut-off of thesupply are carried out at a moment when the pressure of the brake fluidsupplied from the high pressure source to the brake device isapproximately equal to the pressure of the brake fluid supplied from themaster cylinder device to the brake device. That is, where the switchesare carried out at a moment when both pressures are approximately equal,the hydraulic brake force does not change considerably at the switches,whereby the switches can be carried out without giving a driverunfavorable feeling. Therefore, in the pressure receiving piston, apressurized area thereof on which a pressure of the input chamber actsand a pressurized area thereof on which a pressure of the pressurizingchamber acts may be determined such that the pressure of the brake fluidsupplied from the high pressure source and the pressure of the brakefluid supplied from the master cylinder device become almost equal toeach other. In other words, the pressurized area in the input chamberside may be determined smaller than the pressurized area in thepressurizing chamber side by a degree corresponding to the consideredoperation force.

Additionally, even in a condition in which the brake fluid is notintroduced from the high pressure source, where the switch is carriedout so that the master cylinder device becomes the supply source of thebrake fluid to the brake device, the brake device can be actuated by thebrake fluid pressurized depending on only the operation force.Accordingly, for example, in a condition in which the high pressuresource cannot work due to an electric failure etc., a “operation-forcedependent pressurizing state”, that is, a state in which the brake fluidis pressurized depending on only the operation force is realized in themaster cylinder device, and the hydraulic brake force with a magnitudedependent on the operation force generates in the brake device.Therefore, for example, where the shut-off of the supply of the brakefluid from the master cylinder device to the brake device is carried outby the above electromagnetic valve, it is desirable that thiselectromagnetic valve is a normally-opened valve. More specifically,where the electromagnetic valve is a normally-opened valve, it opens ata moment when an electric failure etc. occurs, whereby the brake fluidcan be automatically supplied from the master cylinder device to thebrake device. In addition, where the supply of the brake fluid from thehigh pressure source to the brake device is carried out by the aboveelectromagnetic valve, it is desirable that this electromagnetic valveis a normally-closed valve. More specifically, where the electromagneticvalve is a normally-closed valve, it closes at a moment when an electricfailure etc. occurs, whereby the supply of the brake fluid to the brakedevice can be automatically shut off.

In the master cylinder device of this form, like the above describedInput Piston Free Type Master Cylinder Device, the input piston is notfitted to the pressure receiving piston with any seal. Therefore, amovement of the pressure receiving piston generates no force causing anymovement of the input piston, that is, no force resulting from anyfriction force of any seal to act on the input piston. In other words, amovement of the pressure receiving piston does not pull the input pistonand the operation member. Therefore, operational feeling in a brakeoperation is excellent. In addition, since the input chamber is definedby that the pressure receiving piston is fitted at the main body portionin the housing with the seal and fitted in the partition portion of thehousing with the seal, the seal between the input piston and the housingis not required to be a high-pressure seal. Consequently, a frictionforce resulting from the seal upon a movement of the input piston can becomparatively reduced. That is, a resistance upon a movement of theinput piston is comparatively small, whereby operational feeling in abrake operation is excellent. Especially in the state in which thehydraulic brake force is generated depending on the operation force, itis possible to provide excellent operational feeling.

It is noted that, even in the condition in which the supply source ofthe brake fluid to the brake device is the high pressure source, inother words, even in the condition of master-cut, a driver can move theinput piston forward by a brake operation, and, owing to the operationreaction force by the reaction force applying mechanism, the driver canfeel like that the driver's operation force pressurizes the brake fluidin the pressurizing chamber, that is, the driver operates the brakedevice by the driver's operation force. That is, in the master cylinderdevice, a so-called stroke simulator is constituted by the reactionforce applying mechanism.

(22) The master cylinder device according to the form (21),

wherein the pressure receiving piston includes an extension portionextending from the main body portion through the opening of thepartition portion into the rear side chamber, and is fitted, at theextension portion, in the partition portion with the seal, whereby, theinput chamber is defined, and the inter-piston chamber is defined suchthat a rear end of the extension portion and the input piston face toeach other.

In the master cylinder device of this form, like the above describedInput Piston Free Type Master Cylinder Device having the extensionportion, the inter-piston chamber is defined including a space acrosswhich a rear end face of the extension portion and a front end face ofthe input piston face to each other.

(23) The master cylinder device according to the form (22),

wherein the pressure receiving piston includes a blind hole which isformed inside the main body portion and the extension portion and whichis open rearward, and the inter-piston chamber is defined so as toinclude an interior of the blind hole.

In the master cylinder device of this form, since the inter-pistonchamber is defined utilizing the blind hole, the size of theinter-piston chamber can be comparatively large in the front-backdirection. Therefore, for example, where the master cylinder deviceincludes a mechanism having a spring as the reaction force applyingmechanism, and the spring is housed in the inter-piston chamber, and anelastic reaction force of the spring is applied to the input piston andthe pressure receiving piston, the length of the spring can be set to becomparatively long. Consequently, the constant of the spring can be setcomparatively small.

(24) The master cylinder device according to the form (21),

wherein the partition portion of the housing includes an annularseparation wall portion projecting to inside the housing in a radialdirection and an inner cylindrical portion having a hollow cylindricalshape and extending forward from an inner periphery of the separationwall portion, a front end of the inner cylindrical portion functions asthe opening, and an interior of the inner cylindrical portion serves asa part of the rear side chamber,

wherein the main body portion of the pressure receiving piston includesa blind hole which is open rearward, whereby a rear side portion of themain body portion is a cylindrical portion having a hollow cylindricalshape,

wherein the pressure receiving piston is disposed such that the innercylindrical portion of the partition portion is inserted in thecylindrical portion of the pressure receiving piston, and the pressurereceiving piston and the partition portion are fitted at an innercircumferential face of the cylindrical portion and an outercircumferential face of the inner cylindrical portion to each other withthe seal, whereby the input chamber is defined between a rear end of thecylindrical portion and the separation wall portion of the partitionportion, and

wherein the inter-piston chamber is defined such that a bottom portionof the blind hole of the pressure receiving piston and the input pistonface to each other with the opening formed in the partition portionbeing interposed between the bottom portion and the input piston.

In the master cylinder device of this form, like the above describedInput Piston Free Type Master Cylinder Device constructed to have adouble-cylindrical structure, the housing has a portion outside theinner cylindrical portion, which may be referred to as an outercylindrical portion. In addition, the cylindrical portion of thepressure receiving piston can be considered to be interposed between theinner cylindrical portion and the outer cylindrical portion. Moreover,the input chamber can be considered to be a fluid chamber surrounded ata rear end of the cylindrical portion by the outer cylindrical portion,the separation wall portion, and the inner cylindrical portion.

(25) The master cylinder device according to the form (24),

wherein the input piston is disposed such that at least a part of theinput piston including a front end thereof is inserted in the innercylindrical portion.

(26) The master cylinder device according to the form (25),

wherein the input piston is fitted, at the at least a part of the inputpiston, in the inner cylindrical portion with a seal.

In the master cylinder devices of the above two forms, like the abovedescribed master cylinder device, specifically, the Input Piston FreeType Master Cylinder Device in which at least a part of the input pistonincluding the front end thereof is inserted in the inner cylindricalportion, a part of the pressure receiving piston and a part of the inputpiston overlap with each other in the front-back direction, whereby thetotal length of the master cylinder device can be shortened whilerespective necessary lengths of those pistons are secured. Additionally,in the master cylinder device described in the latter form, where theinput piston is fitted, at a part inserted in the inner cylindricalportion, in the housing with a seal, the inter-piston chamber is definedin the inner cylindrical portion.

(27) The master cylinder device according to any one of the forms(21)-(26),

wherein the reaction force applying mechanism includes a fluid storagechamber communicating with the inter-piston chamber, and anelastic-reaction-force applying mechanism for the fluid storage chamberwhich allows an increase of a volume of the fluid storage chamberaccording to a decrease of a volume of the inter-piston chamber, andwhich applies an elastic reaction force with a magnitude according to anamount of the increase of the volume of the fluid storage chamber to abrake fluid in the fluid storage chamber.

In the master cylinder device of this form, like the Input Piston FreeType Master Cylinder Device having the fluid storage chamber and theelastic-reaction-force applying mechanism for the fluid storage chamber,the elastic reaction force by the elastic-reaction-force applyingmechanism for the fluid storage chamber also acts on the brake fluid inthe inter-piston chamber so as to change the pressure of the brake fluidin the chamber. More specifically, when the input piston moves forwardrelative to the pressure receiving piston, the volume of theinter-piston chamber decreases, and the volume of the fluid storagechamber increases by a volume of the brake fluid decreased in theinter-piston chamber, whereby the elastic reaction force increases.Consequently, the pressure of the brake fluid in the inter-pistonchamber increases, whereby a bias force acting on the input piston tomove the input piston rearward increases. In addition, the increase ofthe pressure of the brake fluid in the inter-piston chamber alsoincreases a bias force acting on the pressure receiving piston to movethe pressure receiving piston forward.

(28) The master cylinder device according to the form (27),

wherein the reaction force applying mechanism includes a reaction forceapplying device disposed outside the housing and having the fluidstorage chamber and the elastic-reaction-force applying mechanism forthe fluid storage chamber.

In the master cylinder device of this form, like the above describedInput Piston Free Type Master Cylinder Device having the reaction forceapplying mechanism, at least a part of the reaction force applyingmechanism is provided outside the housing, whereby a structure insidethe housing can be made comparatively simple.

(29) The master cylinder device according to any one of the forms(21)-(28),

wherein the reaction force applying mechanism is disposed in theinter-piston chamber and includes an elastic member generating anelastic reaction force against the relative forward movement of theinput piston relative to the pressure receiving piston.

For example, a compression coil spring may be employed as the elasticmember. For example, where such a spring is disposed between a face ofthe pressure receiving piston which faces rearward and a face of theinput piston which faces forward, a rearward bias force by the elasticreaction force acts on the input piston upon the forward movement of theinput piston relative to the pressure receiving piston. Therefore, adriver can feel the rearward bias force as the operation reaction force.In addition, a forward bias force acts on the pressure receiving pistonby the elastic reaction force of the spring.

(30) The master cylinder device according to any one of the forms(21)-(29),

wherein the master cylinder device further comprises aninput-piston-relative-forward-movement prohibiting mechanism whichprohibits the relative forward movement of the input piston relative tothe pressure receiving piston.

In the master cylinder device of this form, the operation force can betransmitted to the pressure receiving piston by prohibiting the relativeforward movement of the input piston to the pressure receiving piston.For example, in the master cylinder device in which the elastic membersuch as the spring described above is provided in the inter-pistonchamber, the operation force is transmitted to the pressure receivingpiston while the input piston moves forward relative to the pressurereceiving piston. However, the relative forward movement would cause thebrake operation amount to ineffectively become large. The mastercylinder device of this form may prohibit the relative forward movementof the input piston, when pressurizing the brake fluid depending on theoperation force, so as to transmit the operation force to the pressurereceiving piston without generating an ineffective brake operationamount. This is advantageous particularly in the state in which thehydraulic brake force is generated depending on the operation force.

(31) The master cylinder device according to the form (30),

wherein the input-piston-relative-forward-movement prohibiting mechanismincludes an inter-piston-chamber hermetically closing mechanism whichhermetically closes the inter-piston chamber.

In the master cylinder device of this form, like the above describedInput Piston Free Type Master Cylinder Device having theinter-piston-chamber hermetically closing mechanism, the operation forcecan be transmitted to the pressure receiving piston via the brake fluidin the inter-piston chamber by the inter-piston-chamber hermeticallyclosing mechanism.

(32) The master cylinder device according to any one of the forms(21)-(31),

wherein, in front of the main body portion of the pressure receivingpiston in the front side chamber, there is defined a pressurizingchamber in which the brake fluid to be supplied to the brake device ispressurized by a forward movement of the pressure receiving piston.

The pressurizing chamber of the master cylinder device of this form maybe defined by the pressure receiving piston. Alternatively, for example,another piston etc. may be disposed in front of the pressure receivingpiston, and the pressurizing chamber may be defined by said anotherpiston etc. In other words, the master cylinder device may be configuredsuch that the pressure receiving piston moves forward to push saidanother piston etc. forward. In this master cylinder device, the forwardmovement of the pressure receiving piston can pressurize the brake fluidin the pressurizing chamber.

(33) The master cylinder device according to the form (32),

wherein the master cylinder device further comprises a pressurizingpiston disposed in front of the pressure receiving piston in the frontside chamber,

wherein the pressurizing piston is fitted in the housing with a seal,whereby a pressurizing chamber in which a brake fluid to be supplied tothe brake device is pressurized is defined in front of the pressurizingpiston, and

wherein the master cylinder device is configured such that the forwardmovement of the pressure receiving piston moves forward the pressurizingpiston with the pressure receiving piston abutting on the pressurizingpiston, whereby the brake fluid in the pressurizing chamber ispressurized.

In the master cylinder device of this form, the pressurizing piston ispushed forward by the pressure receiving piston so as to be movedforward, that is, the forward movement of the pressure receiving pistoncan pressurize the brake fluid in the pressurizing chamber. The mastercylinder device of this form is, so to speak, an embodiment in which thepressure receiving piston indirectly pressurizes the brake fluid via thepressurizing piston.

(34) A hydraulic brake system, comprising:

the master cylinder device according to any one of the forms (21)-(33);

a high pressure source device, as the high pressure source, whichintensifies a pressure of a brake fluid; and

a pressure adjusting device which adjusts a pressure of a brake fluid tobe introduced from the high pressure source device to the input chambersof the master cylinder device.

In the hydraulic brake system of this form, the brake fluid from thehigh pressure source device is introduced into the master cylinderdevice via the pressure adjusting device. Alternatively, the brake fluidintroduced into the brake device may be introduced via the pressureadjusting device. In this hydraulic brake system, the hydraulic brakeforce generated in the brake device has a magnitude according to apressure of the pressure-adjusted brake fluid. That is, in the state inwhich the hydraulic brake force is generated depending on thehigh-pressure-source pressure, or in the state in which the hydraulicbrake force is generated depending on the operation force and thehigh-pressure-source pressure, the hydraulic brake force generated inthe brake device can be adjusted by adjusting the pressure of the brakefluid by the pressure adjusting device.

In addition, for the switch described above, that is, the switch of thesupply source of the brake fluid to the brake device between the highpressure source and the master cylinder device, the hydraulic brakesystem may include a switching mechanism. For example, in the hydraulicbrake system described above, that is, in the hydraulic brake systemwhich has a communication passage for supplying the brake fluid from themaster cylinder device to the brake device and an electromagnetic valveprovided in the communication passage as well as a communication passagefor supplying the brake fluid from the high pressure source to the brakedevice and an electromagnetic valve provided in the communicationpassage, the switching mechanism may be constituted by a mechanismhaving those electromagnetic valves as main components.

(35) The hydraulic brake system according to the form (34),

wherein the high pressure source device includes a hydraulic pump whichintensifies the pressure of the brake fluid, and an accumulator whichstores the pressure-intensified brake fluid.

In the hydraulic brake system of this form, like the above describedhydraulic brake system having the hydraulic pump and the accumulator,where the accumulator is configured to store a certain amount of thebrake fluid, the hydraulic pump may be worked only in a time when apressure of the brake fluid in the accumulator is below a predeterminedpressure.

(36) The hydraulic brake system according to the form (34) or (35),

wherein, in front of the main body portion of the pressure receivingpiston in the front side chamber, there is defined a pressurizingchamber in which the brake fluid to be supplied to the brake device ispressurized by a forward movement of the pressure receiving piston,

wherein the pressure adjusting device is configured to be controlled toreduce the pressure of the brake fluid supplied from the high pressuresource device to a pressure according to the control, and configured tosupply the pressure-reduced brake fluid to the master cylinder device,and

wherein the pressure adjusting device includes apilot-pressure-dependent pressure reducing mechanism which utilizes, asa pilot pressure, any one of a pressure of the brake fluid in thepressurizing chamber and a pressure of the brake fluid in theinter-piston chamber, and which reduces the pressure of the brake fluidsupplied from the high pressure source device to a pressure according tothe pilot pressure.

In the hydraulic brake system of this form, like the above describedhydraulic brake system having the pressure adjusting device, thepilot-pressure-dependent pressure reducing mechanism, which is anauxiliary pressure reducing mechanism, can reduce the pressure of thebrake fluid supplied from the high pressure source device.

(37) The hydraulic brake system according to the form (36),

wherein the pilot-pressure-dependent pressure reducing mechanism isconfigured to utilize the pressure of the brake fluid in thepressurizing chamber of the master cylinder device as the pilotpressure.

In the hydraulic brake system of this form, like the above describedhydraulic brake system utilizing the pressure of the pressurizingchamber as the pilot pressure, where the pressure of the brake fluid inthe pressurizing chamber is changed by the operation force, the pressureadjusting device can be activated by utilizing the pressure as the pilotpressure.

(38) The hydraulic brake system according to the form (36),

wherein the pilot-pressure-dependent pressure reducing mechanism isconfigured to utilize the pressure of the brake fluid in theinter-piston chamber of the master cylinder device as the pilotpressure.

In the hydraulic brake system, like the above described hydraulic brakesystem utilizing the pressure of the inter-piston chamber as the pilotpressure, a pressure change of the brake fluid in the inter-pistonchamber can follow a change of a brake operation comparatively well.Therefore, operational feeling in a brake operation is excellent whenthe pressure of the brake fluid is reduced by thepilot-pressure-dependent pressure reducing mechanism.

<<Pressure Receiving Piston Lock Type Master Cylinder Device>>

(41) A master cylinder device for supplying a pressurized brake fluid toa brake device provided in a wheel, comprising:

a housing whose front side end is closed and which includes a partitionportion separating an interior of the housing into a front side chamberand a rear side chamber and having an opening through the partitionportion;

a pressure receiving piston which includes a main body portion having aflange on a rear end thereof and disposed in the front side chamber, andwhich is moved forward by receiving a force for pressurizing the brakefluid to be supplied to the brake device;

a pressurizing piston disposed in the front side chamber and in front ofthe pressure receiving piston; and

an input piston which is disposed in the rear side chamber, which isconnected to a brake operation member disposed behind the housing, andwhich is moved forward by an operation force applied to the brakeoperation member,

wherein the pressurizing piston is fitted in the housing with a seal,the main body portion of the pressure receiving piston is fitted, at theflange and a portion in front of the flange, in the housing withrespective seals, and the pressure receiving piston is fitted in thepartition portion with a seal, whereby: a pressurizing chamber in whichthe brake fluid to be supplied to the brake device is pressurized by aforward movement of the pressurizing piston is defined in front of thepressurizing piston; a first input chamber into which a brake fluid froma high pressure source is introduced is defined between the main bodyportion of the pressure receiving piston and the pressure receivingpiston; a second input chamber into which the brake fluid from the highpressure source is introduced is defined between a rear end of the mainbody portion of the pressure receiving piston and the partition portion;and an opposing chamber which opposes the second input chamber with theflange being interposed between the opposing and second input chambersis defined around the main body portion of the pressure receivingpiston,

wherein the input piston is fitted in the housing with a seal, whereby,between the input piston and the pressure receiving piston, there isdefined an inter-piston chamber across which the input piston and thepressure receiving piston face to each other by utilizing the openingformed in the partition portion though the input piston and the pressurereceiving piston are not fitted to each other with any seal,

wherein the master cylinder device is configured such that a pressurizedarea of the pressure receiving piston on which a pressure of the brakefluid in the first input chamber acts and a pressurized area of thepressure receiving piston on which a pressure of the brake fluid in thesecond input chamber acts are equal, and such that, when the respectivebrake fluids are introduced from the high pressure source into the firstinput chamber and the second input chamber with the opposing chamberbeing hermetically closed, a forward movement of the pressure receivingpiston is prohibited and the brake fluid in the pressurizing chamber ispressurized by the forward movement of the pressurizing piston, and

wherein the master cylinder device further comprises a reaction forceapplying mechanism which is configured to allow a relative forwardmovement of the input piston relative to the pressure receiving pistonby the operation force in a state in which a decrease of a volume of theinter-piston chamber is allowed, and which is configured to apply to thepressure receiving piston and the input piston a reaction force againstthe relative forward movement and with a magnitude according to anamount of the relative forward movement such that the reaction forceacts as an operation reaction force against an operation of the brakeoperation member.

In the master cylinder device of this form, when the brake fluid isintroduced from the high pressure source to the first input chamber, thepressurizing piston moves forward so as to supply the pressurized brakefluid to the brake device. As regards the pressure receiving piston, thepressurized area on which the pressure of the brake fluid in the firstinput chamber acts and the pressurized area on which the pressure of thebrake fluid in the second input chamber acts are equal. Therefore, arearward bias force acting on the pressure receiving piston by thepressure of the brake fluid in the first input chamber and a frontwardbias force acting on the pressure receiving piston by the pressure ofthe brake fluid in the second input chamber become equal. Accordingly,even when the brake fluid is introduced from the high pressure sourceinto the first input chamber and the second input chamber, this brakefluid does not cause any movement of the pressure receiving piston. Inaddition, when the opposing chamber is hermetically closed, the forwardmovement of the pressure receiving piston is prohibited. As a result, ina state in which the opposing chamber is hermetically closed, when adriver operates the brake operation member, the operation force is nottransmitted to the pressurizing piston via the pressure receivingpiston, and the pressurizing piston can pressurize the brake fluid to besupplied to the brake device depending on only a pressure of the brakefluid introduced from the high pressure source. In other words, themaster cylinder device of this form can realize ahigh-pressure-source-pressure dependent pressurizing state. So to say,the master cylinder device can realize the high-pressure-source-pressuredependent pressurizing state with the pressure receiving piston beingfixed (locked), thus the master cylinder device is called the “PressureReceiving Piston Lock Type Master Cylinder Device”.

It is noted that the pressurized area on which the pressure of the brakefluid in the first input chamber acts and the pressurized area on whichthe pressure of the brake fluid in the second input chamber acts neednot be precisely equal but may be slightly different. That is, the term“equal” regarding the pressurized areas of the pressure receiving pistonon which the pressures of the brake fluids act, as used herein, includesa concept that these pressurized areas are slightly different, in otherwords, a concept that these pressurized areas are considered to besubstantially equal. Where the two pressurized areas are slightlydifferent, the magnitude of the forward bias force and the magnitude ofthe rearward bias force described above are slightly different.Therefore, even in a normal condition, the pressure receiving pistonmoves slightly. This is advantageous, for example, to preventing thepressure receiving piston from adhering to the housing, which is causedby that the pressure receiving piston is not moved for a long time.

In addition, where the operation force is transmitted to the pressurereceiving piston by releasing the hermetical closing of the opposingchamber in a realization of the high-pressure-source-pressure dependentpressurizing state, the master cylinder device can realize an“operation-force/high-pressure-source-pressure dependent pressurizingstate”. In this state, the brake device can generate a hydraulic brakeforce with a magnitude dependent on the pressure of the second inputchamber, namely, the high-pressure-source pressure plus a hydraulicbrake force with a magnitude dependent on the operation force. In orderto transmit the operation force from the pressure receiving piston tothe pressure receiving piston, for example, the pressure receivingpiston may be allowed to come into an abutting contact with thepressurizing piston, or alternatively, the first input chamber may behermetically closed. More specifically, where the pressure receivingpiston comes into an abutting contact with the pressurizing piston, theoperation force is transmitted, owing to the abutting contact, from thepressure receiving piston to the pressurizing piston. Where the firstinput chamber is hermetically closed, the operation force istransmitted, via the brake fluid in the first input chamber, to thepressure receiving piston. Therefore, where theoperation-force/high-pressure-source-pressure dependent pressurizingstate is realized in a condition in which a large hydraulic brake forceis required, such as a condition of an emergency brake, the brake devicecan generate a comparatively large hydraulic brake force. In addition,according to the master cylinder device of this form, it is possible togenerate a comparatively large hydraulic brake force with the highpressure source having a comparatively small output. In order totransmit the operation force to the pressure receiving piston, forexample, the input piston may be allowed to come into an abuttingcontact with the pressure receiving piston, or alternatively, theinter-piston chamber may be hermetically closed.

In addition, even when the brake fluid is not introduced from the highpressure source, as in the operation-force/high-pressure-source-pressuredependent pressurizing state, the master cylinder device can realize an“operation-force dependent pressurizing state” by releasing thehermetical closing of the opposing chamber and transmitting theoperation force to the pressurizing piston. Therefore, for example, evenin a condition in which the high pressure source cannot work due to anelectric failure etc., the brake device can be actuated depending ononly the operation force.

In the master cylinder device of this form, like the Input Piston FreeType Master Cylinder Device and the Master-Cut System Adoptable TypeMaster Cylinder Device described above, the input piston is not fittedto the pressure receiving piston with any seal. Therefore, a movement ofthe pressure receiving piston by the introduction of the brake fluidfrom the high pressure source to the input chamber generates no forcecausing any movement of the input piston, that is, no force resultingfrom any friction force of any seal to act on the input piston. In otherwords, a movement of the pressure receiving piston does not pull theinput piston and the operation member. Therefore, operational feeling ina brake operation is excellent. Additionally, in the master cylinderdevice of this form, since the input chamber is defined by that thepressure receiving piston is fitted, at the main body portion, in thehousing with the seal and fitted in the partition portion of the housingwith the seal, the seal between the input piston and the housing is notrequired to be a high-pressure seal. Consequently, a friction forceresulting from the seal upon a movement of the input piston can becomparatively reduced. That is, a resistance upon a movement of theinput piston is comparatively small, whereby operational feeling in abrake operation is excellent. Especially in the operation-forcedependent pressurizing state, it is possible to provide excellentoperational feeling.

Additionally, in the master cylinder device of this form, for example,when the high-pressure-source-pressure dependent pressurizing state isrealized, a force by the pressure of the brake fluid in the pressurizingchamber is not transmitted to the brake operation member. However, owingto the operation reaction force by the reaction force applyingmechanism, the driver can feel like pressurizing the brake fluid in thepressurizing chamber by the driver's operation force, that is, operatingthe brake device. That is, in the master cylinder device of this form, aso-called stroke simulator is constituted by the reaction force applyingmechanism.

(42) The master cylinder device according to the form (41),

wherein the pressure receiving piston includes an extension portionextending from the main body portion through the opening of thepartition portion into the rear side chamber and is fitted, at theextension portion, in the partition portion with the seal, whereby thesecond input chamber is defined, and the inter-piston chamber is definedsuch that a rear end of the extension portion and the input piston faceto each other.

In the master cylinder device of this form, like the Input Piston FreeType Master Cylinder Device and the Master-Cut System Adoptable TypeMaster Cylinder Device having the extension portion as described above,the inter-piston chamber is defined including a space across which arear end face of the extension portion and a front end face of the inputpiston face to each other.

(43) The master cylinder device according to the form (42),

wherein the pressure receiving piston includes a blind hole which isformed inside the main body portion and the extension portion and whichis open rearward, and the inter-piston chamber is defined so as toinclude an interior of the blind hole.

In the master cylinder device of this form, like the above describedMaster Cut System Adoptable Type Master Cylinder Device having the blindhole, since the inter-piston chamber is defined utilizing the blindhole, the size of the inter-piston chamber can be comparatively large inthe front-back direction. Therefore, for example, a comparatively longspring can be employed as the reaction force applying mechanism, and theconstant of the spring can be set to be comparatively small.

(44) The master cylinder device according to the form (43),

wherein the partition portion of the housing includes an annularseparation wall portion projecting to inside the housing in a radialdirection and an inner cylindrical portion having a hollow cylindricalshape and extending forward from an inner periphery of the separationwall portion, a front end of the inner cylindrical portion functions asthe opening, and an interior of the inner cylindrical portion serves asa part of the rear side chamber,

wherein the main body portion of the pressure receiving piston includesa blind hole which is open rearward, whereby a rear side portion of themain body portion is a cylindrical portion having a hollow cylindricalshape, and the main body portion has the flange at a rear end of thecylindrical portion,

wherein the pressure receiving piston is disposed such that the innercylindrical portion of the partition portion is inserted in thecylindrical portion of the pressure receiving piston, and the pressurereceiving piston and the partition portion are fitted at an innercircumferential face of the cylindrical portion and an outercircumferential face of the inner cylindrical portion to each other withthe seal, whereby the second input chamber is defined between the rearend of the cylindrical portion and the separation wall portion of thepartition portion, and

wherein the inter-piston chamber is defined such that a bottom portionof the blind hole of the pressure receiving piston and the input pistonface to each other with the opening formed in the partition portionbeing interposed between the bottom portion and the input piston.

In the master cylinder device of this form, like the Input Piston FreeType Master Cylinder device and the Master-Cut System. Adoptable TypeMaster Cylinder described above whose respective housings areconstructed to have a double-cylindrical structure, the housing has aportion outside the inner cylindrical portion, which may be referred toas an outer cylindrical portion. The cylindrical portion of the pressurereceiving piston can be considered to be interposed between the innercylindrical portion and the outer cylindrical portion. Moreover, theinput chamber can be considered to be a fluid chamber surrounded at arear end of the cylindrical portion by the outer cylindrical portion,the separation wall portion, and the inner cylindrical portion.

(45) The master cylinder device according to the form (44),

wherein at least a part of the input piston including a front endthereof is disposed so as to be inserted in the inner cylindricalportion.

(46) The master cylinder device according to the form (45),

wherein the input piston is fitted, at the at least a part of the inputpiston, in the inner cylindrical portion with a seal.

In the master cylinder devices of the above two forms, like the abovedescribed master cylinder devices, specifically, the Input Piston FreeType Master Cylinder Device and the Master-Cut System Adoptable TypeMaster Cylinder Device in each of which at least a part of the inputpiston including a front end thereof is inserted in the innercylindrical portion, a part of the pressure receiving piston and a partof the input piston overlap with each other in the front-back direction,whereby a total length of the master cylinder device can be shortenedwhile respective necessary lengths of those pistons are secured.Additionally, in the master cylinder device described in the latterform, where the input piston is fitted, at a part inserted in the innercylindrical portion, in the housing with a seal, the inter-pistonchamber is defined in the inner cylindrical portion.

(47) The master cylinder device according to any one of the forms(41)-(46),

wherein the reaction force applying mechanism includes an elastic memberdisposed in the inter-piston chamber and generating an elastic reactionforce against a relative forward movement of the input piston relativeto the pressure receiving piston.

In the master cylinder device of this form, like the above describedMaster-Cut System Adoptable Type Master Cylinder Device in which thereaction force applying mechanism includes the elastic member, forexample, a compression coil spring may be employed as the elasticmember. Such a spring can apply a rearward bias force by the elasticreaction force to the input piston against the forward movement of theinput piston relative to the pressure receiving piston. Therefore, adriver can feel the bias force as the operation reaction force.

(48) The master cylinder device according to any one of the forms(41)-(47),

wherein the master cylinder device further comprises alow-pressure-source communication mechanism which allows the opposingchamber to communicate with a low pressure source, and

wherein the master cylinder device is configured to allow the forwardmovement of the pressure receiving piston in a state in which theopposing chamber communicates with the low pressure source by thelow-pressure-source communication mechanism so as to allow an abuttingcontact of the pressure receiving piston and the pressurizing piston toeach other, and is configured to allow a pressurization of the brakefluid in the pressurizing chamber not depending on pressures of thebrake fluids introduced from the high pressure source into the firstinput chamber and the second input chamber but depending on theoperation force.

In the master cylinder device of this form, the operation force istransmitted to the pressurizing piston via the pressure receiving pistonby a function of the low-pressure-source communication mechanism.Therefore, the low-pressure-source communication mechanism may beconsidered a mechanism for realizing the operation-force dependentpressurizing state. In addition, when the brake fluid from the highpressure source is introduced into the second input chamber in a statein which the pressure receiving piston abuts on the pressurizing pistonby the low-pressure-source communication mechanism, the pressurizingpiston can be moved forward depending on a pressure of the brake fluidin the second input chamber, whereby theoperation-force/high-pressure-source-pressure dependent pressurizingstate is realized. In order to allow the pressurization of the brakefluid in the pressurizing chamber by the operation force, for example,as described above, the input piston may be allowed to come into anabutting contact with the pressure receiving piston, or alternatively,the inter-piston chamber may be hermetically closed.

For example, a mechanism having a normally-opened electromagnetic valveas a main component may be employed as the low-pressure-sourcecommunication mechanism. That is, in a case in which the master cylinderdevice is configured to make the opposing chamber communicate with thelow pressure source by opening a valve, the normally-opened valve openssimultaneously at a moment when an electric failure occurs, and then theopposing chamber communicates with the low pressure source. In otherwords, such a low-pressure-source communication mechanism can allow themaster cylinder device to be actuated in the operation-force dependentpressurizing state in an electric failure condition.

(49) The master cylinder device according to any one of the forms(41)-(48),

wherein the master cylinder device further comprises aninput-piston-relative-forward-movement prohibiting mechanism whichprohibits the relative forward movement of the input piston relative tothe pressure receiving piston.

In the master cylinder device of this form, like the above describedMaster-Cut System Adoptable Type Master Cylinder Device having theinput-piston-relative-forward-movement prohibiting mechanism, theoperation force can be transmitted to the pressure receiving piston byprohibiting the relative forward movement of the input piston to thepressure receiving piston. Accordingly, since it does not occur that theinput piston moves forward relative to the pressure receiving piston andthe operation force is transmitted to the pressure receiving piston, theoperation force can be transmitted to the pressure receiving pistonwithout generating an ineffective brake operation amount when the brakefluid is pressurized in the operation-force dependent pressurizing stateor the operation-force/high-pressure-source-pressure dependentpressurizing state, that is, depending on the operation force. Thisfeature is advantageous in the operation-force dependent pressurizingstate in particular.

(50) The master cylinder device according to the form (49),

wherein the input-piston-relative-forward-movement prohibiting mechanismincludes an inter-piston-chamber hermetically closing mechanism whichhermetically closes the inter-piston chamber.

In the master cylinder device of this form, like the Input Piston FreeType Master Cylinder Device and the Master-Cut System Adoptable TypeMaster Cylinder Device described above which have theinter-piston-chamber hermetically closing mechanism, the operation forcecan be transmitted to the pressure receiving piston via the brake fluidin the inter-piston chamber by the inter-piston-chamber hermeticallyclosing mechanism.

(51) A hydraulic brake system, comprising:

the master cylinder device according to any one of the forms (41)-(50);

a high pressure source device, as the high pressure source, whichintensifies a pressure of a brake fluid; and

a pressure adjusting device which adjusts a pressure of a brake fluid tobe introduced from the high pressure source device to the input chambersof the master cylinder device.

In the master cylinder device of this form, like the above describedhydraulic brake system having the Input Piston Free Type Master CylinderDevice, the high pressure source device, and pressure adjusting device,the pressure of the brake fluid in the pressurizing chamber can beadjusted to a pressure according to a pressure of the pressure-adjustedbrake fluid in the high-pressure-source-pressure dependent pressurizingstate and the operation-force/high-pressure-source-pressure dependentpressurizing state. In other words, the hydraulic brake force in thebrake device can be adjusted.

(52) The hydraulic brake system according to the form (51),

wherein the high pressure source device includes a hydraulic pump whichintensifies the pressure of the brake fluid, and an accumulator whichstores the pressure-intensified brake fluid.

In the hydraulic brake system of this form, like the above describedhydraulic brake system having the hydraulic pump and the accumulator,where the accumulator is configured to store a certain amount of thebrake fluid, the hydraulic pump may be worked only in a time when apressure of the brake fluid in the accumulator is below a predeterminedpressure.

(53) The hydraulic brake system according to the form (51) or (52),

wherein the pressure adjusting device is configured to be controlled toreduce the pressure of the brake fluid supplied from the high pressuresource device to a pressure according to the control, and configured tosupply the pressure-reduced brake fluid to the master cylinder device,and

wherein the pressure adjusting device includes apilot-pressure-dependent pressure reducing mechanism which utilizes, asa pilot pressure, any one of a pressure of the brake fluid in thepressurizing chamber, a pressure of the brake fluid in the opposingchamber, and a pressure of the brake fluid in the inter-piston chamber,and which reduces the pressure of the brake fluid supplied from the highpressure source device to a pressure according to the pilot pressure.

In the hydraulic brake system of this form, like the above describedhydraulic brake system having the pressure adjusting device, thepilot-pressure-dependent pressure reducing mechanism, which is anauxiliary pressure reducing mechanism, can reduce the pressure of thebrake fluid supplied from the high pressure source device.

(54) The hydraulic brake system according to the form (53),

wherein the pilot-pressure-dependent pressure reducing mechanism isconfigured to utilize the pressure of the brake fluid in thepressurizing chamber of the master cylinder device as the pilotpressure.

In the hydraulic brake system of this form, like the above describedhydraulic brake system utilizing the pressure of the pressurizingchamber as the pilot pressure, where the pressure of the brake fluid inthe pressurizing chamber is changed by the operation force, the pressureadjusting device can be activated by utilizing the pressure as the pilotpressure.

(55) The hydraulic brake system according to the form (53),

wherein the pilot-pressure-dependent pressure reducing mechanism isconfigured to utilize the pressure of the brake fluid in thepressurizing chamber of the master cylinder device as the pilotpressure.

In the hydraulic brake system, like the above described hydraulic brakesystem utilizing the pressure of the inter-piston chamber as the pilotpressure, a pressure change of the brake fluid in the inter-pistonchamber can follow a change of a brake operation comparatively well.Therefore, operational feeling in a brake operation is excellent whenthe pressure of the brake fluid is reduced by thepilot-pressure-dependent pressure reducing mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a drive system and a brake system of ahybrid vehicle equipped with a master cylinder device of an embodimentaccording to the claimable invention.

FIG. 2 is a view of a hydraulic brake system including the mastercylinder device of a first embodiment.

FIG. 3 is a view of a pressure-intensifying/reducing device in thehydraulic brake system illustrated in FIG. 2 for adjusting a pressure ofa brake fluid intensified by the high pressure source.

FIG. 4 is a view of a reaction force applying mechanism employed in themaster cylinder device illustrated in FIG. 2.

FIG. 5 is a view of a hydraulic brake system including the mastercylinder device of a second embodiment.

FIG. 6 is a view of a hydraulic brake system including the mastercylinder device of a third embodiment.

FIG. 7 is a view of a hydraulic brake system including the mastercylinder device of a fourth embodiment.

FIG. 8 is a view of a hydraulic brake system including the mastercylinder device of a fifth embodiment.

FIG. 9 is a view of a hydraulic brake system including the mastercylinder device of a sixth embodiment.

FIG. 10 is a view of a hydraulic brake system including the mastercylinder device of a seventh embodiment.

FIG. 11 is a view of a hydraulic brake system including the mastercylinder device of a eighth embodiment.

FIG. 12 is a view of a hydraulic brake system including the mastercylinder device of a ninth embodiment.

FIG. 13 is a view of a hydraulic brake system including the mastercylinder device of a tenth embodiment.

MODES FOR CARRYING OUT THE INVENTION

There will be described in detail some embodiments according to theclaimable invention with reference to the drawings. It is to beunderstood, however, that the claimable invention is not limited to thefollowing embodiments but may be embodied with various changes andmodifications on the basis of knowledge of those skilled in the art.

First Embodiment Structure of Vehicle

FIG. 1 schematically illustrates a drive system and a brake system of ahybrid vehicle equipped with a master cylinder device of a firstembodiment. The vehicle is equipped with an engine 10 and an electricmotor 12 as power sources, and also an electric generator 14 forgenerating electricity by an output power of the engine 10. The engine10, the electric motor 12, and the electric generator 14 are connectedto one another via a power-distribution mechanism 16. By controlling thepower-distribution mechanism 16, the power of the engine 10 can bedivided into a power for driving the electric generator 14 and a powerfor rotating drive wheels among four wheels 18, and a power of theelectric motor 12 can be transmitted to the drive wheels. In otherwords, the power-distribution mechanism 16 functions as a speed-changemechanism with respect to a driving power which is transmitted to thedrive wheels via a speed reducer 20 and a drive shaft 22. It is notedthat, while some of components such as the wheels 18 are collectivelydescribed, a suitable one of suffixes “FL”, “FR”, “RL”, “RR”respectively indicative of a front left wheel, a front right wheel, arear left wheel, and a rear right wheel is attached to the numerals of acomponent element, where it is needed to indicate which one of the fourwheels the component corresponds to. According to the explanation of thesuffixes, the drive wheels of the vehicle are the wheel 18RL and thewheel 18 RR.

The electric motor 12 is an alternate current (AC) synchronous motor andis driven by AC electricity. The vehicle is equipped with an inverter 24which can change electricity of direct current to electricity ofalternate current and vice versa. Therefore, by controlling the inverter24, electricity of alternate current generated by the electric generator14 can be inverted into electricity of direct current for being chargedin a battery 26, and electricity of direct current charged in thebattery 26 can be inverted into electricity of alternate current fordriving the electric motor 12. The electric generator 14 is constructedas an AC synchronous motor, like the electric motor 12. Accordingly, thevehicle of the present embodiment can be considered to have two ACsynchronous motors. One of them is used as the electric motor 12 tomainly output the driving power, and the other of them is used as theelectric generator 14 to mainly generate electricity by using the outputpower of the engine 10.

The electric motor 12 can also generate (regenerate) electricity byusing rotations of the wheels 18RL and 18RR in the vehicle running. Inregenerating electricity, the electric motor 12 connected to the wheels18RL and 18RR generates electricity and a resistance force forrestraining a rotation of the electric motor 12. Therefore, it ispossible to utilize the resistance force as a brake force for brakingthe vehicle. That is, the electric motor 12 is utilized as means of aregenerative brake which brakes the vehicle while regeneratingelectricity. Thus, the vehicle is braked by controlling the regenerativebrake as well as an engine brake and a hydraulic brake described below.On the other hand, the electric generator 14 mainly generateselectricity by using the output power of the engine 10 and alsofunctions as an electric motor by that electricity is supplied from thebattery 26 via the inverter 24.

In the vehicle, a control of the above brakes and various other controlsassociated with the vehicle are executed by a plurality of electroniccontrol units (ECUs). Among the ECUs, a main ECU 30 has a function forsupervising the execution of these controls. For instance, the hybridvehicle can run by a drive of the engine 10 and a drive of the electricmotor 12, which are synthetically controlled by the main ECU 30.Specifically, the main ECU 30 determines a ratio between the outputpower of the engine 10 and an output power of the electric motor 12,and, on the basis of the ratio, the main ECU 30 sends, to an engine ECU32 for controlling the engine 10 and a motor ECU 34 for controlling theelectric motor 12 and the electric generator 14, commands regardingtheir respective controls.

A battery ECU 36 for controlling the battery 26 is also connected to themain ECU 30. The battery ECU 36 monitors an electric charge state of thebattery 26, and sends a charge-request command to the main ECU 30 whenan electric charge amount is short. When the main ECU 30 receives thecharge-request command, the main ECU 30 sends, to the motor ECU 34, acommand of generating electricity by the electric generator 14 in orderto charge the battery 26.

A brake ECU 38 is also connected to the main ECU 30. The vehicle isequipped with a brake operation member (hereinafter, referred to as an“operation member”, where appropriate) operated by a driver. The brakeECU 38 determines a target brake force on the basis of at least one of abrake operation amount (hereinafter, referred to as an “operationamount”, where appropriate) which is an amount of operation of theoperation member and a brake operation force (hereinafter, referred toas an “operation force”, where appropriate) which is a force that isapplied to the operation member by the driver, and sends the targetbrake force to the main ECU 30. The main ECU 30 sends the target brakeforce to the motor ECU 34, and then the motor ECU 34 controls theregenerative brake on the basis of the target brake force and sends, tothe main ECU 30, an execution value, that is, a value of theregenerative brake force which is being generated. In the main ECU 30,the regenerative brake force is subtracted from the target brake force,and a target hydraulic brake force which should be generated in ahydraulic brake system 40 provided in the vehicle is determined on thebasis of the remainder. The main ECU 30 sends the target hydraulic brakeforce to the brake ECU 38, and then the brake ECU 38 controls thehydraulic brake system 40 such that a hydraulic brake force generated bythe hydraulic brake system 40 becomes equal to the target hydraulicbrake force.

<<Structure of Hydraulic Brake System>>

The hydraulic brake system 40 provided in the hybrid vehicle constructedas described above will be described with reference to FIG. 2. In thefollowing description, the terms “forward” and “rearward” are used toindicate the leftward direction and the rightward direction in FIG. 2,respectively. In addition, the terms “front side”, “front end”, “forwardmovement”, “rear side”, “rear end”, “rearward movement”, etc. are usedfor similar indication. Incidentally, in the following description,characters enclosed in square brackets [ ] represent sensors etc. in thedrawings.

FIG. 2 schematically represents the hydraulic brake system 40 providedin the vehicle. The hydraulic brake system 40 has a master cylinderdevice 50 for pressurizing a brake fluid. The driver in the vehicle canactuate the master cylinder device 50 by operating an operation device52 which is connected to the master cylinder device 50. The mastercylinder device 50 pressurizes the brake fluid by its actuation. Thepressurized brake fluid is supplied to each of the brake devices 56provided in the respective wheels via an antilock device 54 connected tothe master cylinder device 50. The brake devices 56 generate respectiveforces for restraining rotations of the wheels 18, namely, hydraulicbrake forces, depending on a pressure of the pressurized brake fluid(hereinafter, referred to as a “master pressure”, where appropriate).

The hydraulic brake system 40 has, as a high pressure source, ahigh-pressure-source device 58 for intensifying a pressure of a brakefluid. The high-pressure-source device 58 is connected to the mastercylinder device 50 via a pressure-intensifying/reducing device 60. Thepressure-intensifying/reducing device 60 is a device which controls thepressure of the brake fluid intensified by the high-pressure-sourcedevice 58 (hereinafter, referred to as a “high-pressure-sourcepressure”, where appropriate) to be not higher than the pressure, andwhich intensifies and reduces the pressure of the brake fluid inputtedto the master cylinder device 50. This pressure is referred to as an“input pressure”, where appropriate. That is, the input pressure is apressure obtained by controlling the brake fluid of thehigh-pressure-source pressure, and may be called a controlledhigh-pressure-source pressure. The master cylinder device 50 isconstructed to be able to be actuated according to the intensificationand reduction of the input pressure. The hydraulic brake system 40 has areservoir 62, as a low pressure source, for storing a brake fluid at theatmospheric pressure. The reservoir 62 is connected to the mastercylinder device 50, the pressure-intensifying/reducing device 60, andthe high-pressure-source device 58.

The operation device 52 includes a brake pedal 70 as an operation memberand an operation rod 72 connected to the brake pedal 70. The brake pedal70 is pivotably held at an upper end portion thereof on the body of thevehicle. The operation rod 72 is connected at a rear end portion thereofto the brake pedal 70 and at a front end portion thereof to the mastercylinder device 50. The operation device 52 also has an operation amountsensor [SP] 74 for detecting the operation amount of the brake pedal 70and an operation force sensor [FP] 76 for detecting the operation force.The operation amount sensor 74 and the operation force sensor 76 areconnected to the brake ECU 38 which determines the target brake force onthe basis of values detected by the sensors.

The brake devices 56 are connected to the master cylinder device 50 viafluid passages 80, 82. The fluid passages 80, 82 are fluid passages forsupplying, to the brake devices 56, the brake fluid pressurized to themaster pressure by the master cylinder device 50. An master pressuresensor [P_(O)] 84 is provided on the fluid passage 80. Though detailedexplanation about the brake devices 56 is abbreviated, each of themincludes a brake caliper, a wheel cylinder (brake cylinder) and brakepads which are provided in the brake caliper, and a brake disc whichrotates together with the corresponding wheel. Each of the fluidpassages 80, 82 is connected to the brake cylinder of each brake device56. On the way of each of the fluid passages 80, 82, there is providedthe antilock device 54. Incidentally, the fluid passage 80 is connectedto the brake devices 56RL, 56RR for the rear wheels, and the fluidpassage 82 is connected to the brake devices 56FL, 56FR for the frontwheels. In each of the brake devices 56, the brake cylinder presses thebrake pad onto the brake disk on the basis of the master pressure, andthen friction resulting from the press generates the hydraulic brakeforce for restraining rotation of the corresponding wheel, whereby thevehicle is braked.

The antilock device 54 is a common device and, in short, has four pairsof open/close valves corresponding to the respective wheels. One of theopen/close valves of each of the pairs is a pressure-intensifyingopen/close valve, and is put in an open state, when the correspondingwheel is not locked. The other of them is an pressure-reducingopen/close valve, and is put in a close state, when the wheel is notlocked. The antilock device 54 is configured such that, when the wheelis locked, the pressure-intensifying open/close valve shuts off a flowof the brake fluid from the master cylinder device 50 to the brakedevices 56 and the pressure-reducing open/close valve allows a flow ofthe brake fluid from the brake devices 56 to the reservoir 62, so as torelease the lock of the wheel.

The high-pressure-source device 58 includes a hydraulic pump 90 whichsuctions the brake fluid from the reservoir 62 and intensifies thepressure of the brake fluid, and an accumulator 92 in which thepressure-intensified brake fluid is stored. Incidentally, the hydraulicpump 90 is driven by an electric motor 94. The high-pressure-sourcedevice 58 has a high-pressure-source pressure sensor [Ph] 96 fordetecting the pressure of the pressure-intensified brake fluid. Thebrake ECU 38 monitors a value detected by the high-pressure-sourcepressure sensor 96, and the hydraulic pump 90 is controlled to be drivenon the basis of the detected value. Owing to the control, thehigh-pressure-source device 58 supplies, to thepressure-intensifying/reducing device 60, the brake fluid having apressure of a predetermined pressure at all times.

The pressure-intensifying/reducing device 60 includes a pressureadjusting valve device 100 which adjusts the pressure of the brake fluidsupplied from the high pressure source device 58 according to a pressureof the brake fluid introduced into the pressure adjusting valve device100, an electromagnetic pressure-intensifying linear valve 102 connectedwith the high pressure source device 58, and an electromagneticpressure-reducing linear valve 104 connected with the reservoir 62. Thepressure adjusting valve device 100 is connected to the electromagneticpressure-intensifying linear valve 102 and the electromagneticpressure-reducing linear valve 104 within thepressure-intensifying/reducing device 60. The activations of theelectromagnetic pressure-reducing linear valve 102 and theelectromagnetic pressure-reducing linear valve 104 controls the pressureof the brake fluid from the high pressure source device 58 and suppliesit to the pressure adjusting valve device 100. The pressure adjustingvalve device 100 is activated according to the pressure of the brakefluid and adjusts the pressure of the brake fluid from the high pressuresource device 58, and thus can supply the brake fluid to the mastercylinder device 50.

The pressure adjusting valve device 100 has, as illustrated in FIG. 3, ahousing 110 whose both ends are closed and which has a hollowcylindrical shape, a first plunger 112 disposed inside the housing 110and having a solid cylindrical shape, a second plunger 114 disposedbelow the first plunger 112 and having a solid cylindrical shape, and apressure adjusting pipe 116 disposed above the first plunger 112 andhaving a hollow cylindrical shape. These first plunger 112, secondplunger 114, and pressure adjusting pipe 116 are slidably fitted in thehousing 110, independently. The housing 110 has step faces on the innercircumferential face thereof because the internal diameter thereof isdifferent according to location. The internal diameter is generallylarger at a higher location. In addition, the first plunger 112, thesecond plunger 114, and the pressure adjusting pipe 116 also haverespective step faces on their respective outer periphery because theouter diameter of each of them varies according to location. Thepressure adjusting pipe 116 has a through hole 118 being through thepressure adjusting pipe 116 in an axis direction and a radial direction,and has respective openings of the through hole 118 at an upper endface, a lower end face, and a side face. On the opening at the lower endface of the pressure adjusting pipe 116, an upper end portion of thefirst plunger 112 can be seated. On the other hand, a pin 120 supportedby an upper end face of the housing 110 is fitted in the opening at theupper end face of the pressure adjusting pipe 116. The pressureadjusting pipe 116 can move relative to the pin 120. In addition, abovethe pressure adjusting pipe 116, there is provided an annular bufferrubber 122 for preventing the pressure adjusting pipe 116 from cominginto an abutting contact with the housing 110. Between the first plunger112 and the pressure adjusting pipe 116, there is provided a spring 124being a compression spring, which biases the first plunger 112 and thepressure adjusting pipe 116 to be separated from each other. Between thepressure adjusting pipe 116 and the housing 110, there is provided aspring 126 being a compression spring, which biases the pressureadjusting pipe 116 downward.

Inside the housing 110, there are formed a plurality of fluid chambersby the inner circumferential face and end faces of the housing 110, andouter circumferential faces and end faces of the first plunger 112, thesecond plunger 114, and the pressure adjusting pipe 116. Specifically, afirst fluid chamber 130 is defined between a lower end face of thesecond plunger 114 and an inner bottom face of the housing 110, and asecond fluid chamber 132 is defined between an upper end face of thesecond plunger and a lower end face of the first plunger 112. The outerdiameter of an upper portion of the pressure adjusting pipe 116 issmaller than the inner diameter of the housing 110, whereby a thirdfluid chamber 134 is defined between the pressure adjusting pipe 116 andthe housing 110. The outer diameter of a lower portion of the pressureadjusting pipe 116 is slightly smaller than the inner diameter of thehousing 110, whereby a fourth fluid chamber 136 is defined between thepressure adjusting pipe 116 and the housing 110. Moreover, a fifth fluidchamber 138 is defined by an outer circumferential face of an upperportion of the first plunger 112, a lower end face of the pressureadjusting pipe 116, and the inner circumferential face of the housing110.

These fluid chambers communicate with the exterior through communicationholes provided in the housing 110. Specifically, the first fluid chamber130 is connected to a fluid passage diverging from the fluid passage 80,and thus the brake fluid pressurized by the master cylinder device 50 tothe master pressure is supplied to the first fluid chamber 130. Thesecond fluid chamber 132 is connected to the electromagneticpressure-intensifying linear valve 102 and the electromagneticpressure-reducing linear valve 104, and thus a brake fluid in the secondfluid chamber 132 has the pressure adjusted by the electromagneticpressure-intensifying linear valve 102 and the electromagneticpressure-reducing linear valve 104. The fourth fluid chamber 136 isconnected to the high pressure source device 58, and thus a brake fluidin the fourth fluid chamber 136 has the high-pressure-source pressure.The fifth fluid chamber 138 is connected to the reservoir 62, and thus abrake fluid in the fifth fluid chamber 138 has the atmospheric pressure.A pressure of a brake fluid in the third fluid chamber 134, as describedlater, is adjusted by the activation of the pressure adjusting valvedevice 100. In addition, the third fluid chamber 134 is connected to themaster cylinder device 50, and thus the pressure-adjusted brake fluid isinputted into the master cylinder device 50. In other words, thepressure of the brake fluid in the third fluid chamber 134 is the inputpressure for the master cylinder device 50.

The pressure of the brake fluid in the third fluid chamber 134 isnormally adjusted according to the pressure of the brake fluid suppliedto the second fluid chamber 132 (hereinafter, referred to as a“controlling fluid pressure”, where appropriate). The controlling fluidpressure is intensified or reduced by controlling the electricitysupplied to the electromagnetic pressure-intensifying linear valve 102and the electromagnetic pressure-reducing linear valve 104. When theelectricity is not supplied to the electromagnetic pressure-intensifyinglinear valve 102 and the electromagnetic pressure-reducing linear valve104, the electromagnetic pressure-intensifying linear valve 102 isclosed and the electromagnetic pressure-reducing linear valve 104 isopened, and thus the controlling fluid pressure becomes the atmosphericpressure. When the maximum electric current in a predetermined range issupplied to the electromagnetic pressure-reducing linear valve 104 andan electricity supplied to the electromagnetic pressure-intensifyinglinear valve 102 is controlled, a valve opening pressure of theelectromagnetic pressure-intensifying linear valve 102 is controlledwith the electromagnetic pressure-reducing linear valve 104 beingclosed. In this control, the controlling fluid pressure is increased asthe electricity supplied to the electromagnetic pressure-intensifyinglinear valve 102 is increased. On the other hand, when the electricityis not supplied to the electromagnetic pressure-intensifying linearvalve 102 and the electricity to the electromagnetic pressure-reducinglinear valve 104 is controlled, a valve opening pressure of theelectromagnetic pressure-reducing linear valve 104 is controlled withthe electromagnetic pressure-intensifying linear valve 102 being closed.In this control, the controlling fluid pressure is reduced as theelectricity supplied to the electromagnetic pressure-reducing linearvalve 104 is reduced.

The increase of the controlling fluid pressure, as described above,causes the first plunger 112 to move upward against an elastic force ofthe coil spring 124 so as to be seated on the opening of the throughhole 118 at the lower end of the pressure adjusting pipe 116. Thisopening is referred to as a “fifth-fluid-chamber side opening”, whereappropriate. Further upward movement of the first plunger 112 causes thepressure adjusting pipe 116 to move upward, thereby separating a stepface 140 on the outer circumferential face of the pressure adjustingpipe 116 from the step face formed on an inner periphery portion of thehousing 110. Therefore, a flow of the brake fluid from the fourth fluidchamber 136 to the third fluid chamber 134 is allowed, whereby apressure of the third fluid chamber increases. In addition, thereduction of the controlling fluid pressure causes the step face 140 ofthe pressure adjusting pipe 116 to be seated on the step face 142 of thehousing 110 with the first plunger 112 being seated on thefifth-fluid-chamber side opening. Further reduction of the controllingfluid pressure causes the first plunger to separate from thefifth-fluid-chamber side opening, whereby the third fluid chamber 134 iscommunicated with the reservoir 62 via the fifth fluid chamber 138. Thatis, the pressure-intensifying/reducing device 60 is a pressure adjustingdevice in which the electromagnetic pressure-intensifying linear valve102 and the electromagnetic pressure-reducing linear valve 104 arecontrolled to reduce the pressure of the brake fluid supplied from thehigh pressure source device to a pressure according to the control, andwhich supplies the pressure-reduced brake fluid to the master cylinderdevice 50.

In addition, the pressure adjusting valve device 100 is configured so asto be able to intensify or reduce the brake fluid in the third fluidchamber 134 depending on a pressure of the brake fluid in the firstfluid chamber 130, that is, the master pressure generated by theactuation of the master cylinder device 50 in a condition in which theelectromagnetic pressure-intensifying linear valve 102 and theelectromagnetic pressure-reducing linear valve 104 are not supplied withthe electricity. Accordingly, as the pressure of the brake fluid in thefirst fluid chamber 130 increases, the second plunger 114 moves upward,whereby the first plunger 112 is moved upward too. Also, as the pressureof the brake fluid in the first fluid chamber 130 reduces, the secondplunger 114 moves downward, whereby the first plunger 112 moves downwardtoo. Therefore, as described above, the pressure of the brake fluid inthe third fluid chamber 134 is increased and reduced in association withthe increase and reduction of the pressure of the brake fluid in thefirst fluid chamber 130. That is, the pressure adjusting valve device100 can be activated by utilizing the above master pressure as a pilotpressure, and has a pilot-pressure-dependent pressure reducing mechanismfor reducing the pressure of the brake fluid supplied from the highpressure source device to a pressure according to the pilot pressure.

<<Structure of Master Cylinder Device>>

The master cylinder device 50 is categorized into the Input Piston FreeType Master Cylinder Device, and has a housing 150 being a casing, afirst pressurizing piston 152 and a second pressurizing piston 154 whichpressurize the brake fluid to be supplied to the brake devices 56, andan input piston 156 to which an operation of the driver is inputted viathe operation device 52. FIG. 2 shows a state in which the mastercylinder device 50 is not actuated, that is, a brake operation is notperformed. It is noted that each of all figures of master cylinderdevices of embodiments described in the following shows a state in whicha brake operation is not carried out.

The housing 150 mainly includes three members, specifically, a firsthousing member 160, a second housing member 162, and a third housingmember 164. The first housing member 160 has a roughly hollowcylindrical shape whose front end is closed. The first housing member160 is sectioned into two portions having mutually different innerdiameters, specifically, a front small-diameter portion 166 arranged ina front side and having a small inner diameter, and a rearlarge-diameter portion 168 arranged in a rear side and having a largeinner diameter. The second housing member 162 has a roughly hollowcylindrical shape, and is sectioned into three portions having mutuallydifferent inner diameters, specifically, a front large-diameter portion170 arranged in a front side and having a large inner diameter, a rearsmall-diameter portion 172 arranged in a rear side and having a smallinner diameter, and an intermediate portion 174 arranged between theabove two portions and having an inner diameter of a medium size betweenthe above two inner diameters. The second housing member 162 is unitedwith the first housing member 160 by that a rear end portion of the rearlarge-diameter portion 168 of the first housing member 160 is insertedinto an interior of the front large-diameter portion 170. By the way,the second housing member 162 has a flange 176 on an outer peripherythereof, and the master cylinder device 50 is fixed on a vehicle body atthe flange 176. Between a rear end face of the first housing member 160and a step face formed between the rear small-diameter portion 172 andintermediate portion 174 of the second housing member 162, there isinterposed the third housing member 164 having a disk shape. In thecenter of the third housing member 164, there is provided a through hole178. Therefore, an interior of the housing 150 constructed above isseparated by the third housing member 164 into a front side chamber R1located in a front side and a rear side chamber R2 located in a rearside. That is, the third housing member 164 serves as a partitionportion separating the interior of the housing 150, and the through hole178 serves as an opening of the partition portion.

The second pressurizing piston 154 has a hollow cylindrical shape whoserear end portion is closed, and is slidably fitted with seals in thefront small-diameter portion 166 of the first housing member 160 in thefront side chamber R1. The first pressurizing piston 152 includes a mainbody portion 180 located in the front side chamber R1 and having ahollow cylindrical shape whose rear end portion is closed, and anextension portion 182 extending from a rear end portion of the main bodyportion 180 through the through hole 178 into the rear side chamber R2.Additionally, on an outer periphery of a bottom portion of the main bodyportion 180, there is provided a flange 184. The first pressurizingpiston 152 is fitted with seals in the housing 150 such that a frontportion of the main body portion 180 slidably contacts with the frontsmall-diameter portion 166 of the first housing member 160, the flange184 slidably contacts with the rear large-diameter portion 168 of thefirst housing member 160, and the extension portion 182 slidablycontacts with the through hole 178 of the third housing member 164.

In front of the first pressurizing piston 152 and between the firstpressurizing piston 152 and the second pressurizing piston 154, there isdefined a first pressurizing chamber R3 in which the brake fluid ispressurized to be supplied to the brake devices 56RL, RR provided in thetwo rear wheels. And in front of the second pressurizing piston 154,there is defined a second pressurizing chamber R4 in which the brakefluid is pressurized to be supplied to the brake devices 56FL, FRprovided in the two front wheels. Incidentally, a headed pin 186 isscrewed vertically on a bottom portion of a blind hole being openforward, and a pin-retaining tube 188 is fixed on a rear end face of thesecond pressurizing piston 154. These headed pin 186 and pin-retainingtube 188 limits a distance in which the first pressurizing piston 302and the second pressurizing piston 304 separate from each other to bewithin a predetermined rang. In the first pressurizing chamber R3 andthe second pressurizing chamber R4, compression coil springs(hereinafter, referred to as a “return springs”, where appropriate) 190,192 are disposed, respectively. Those springs bias the firstpressurizing piston 152 and the second pressurizing piston 154 indirections that the pistons 152, 154 separate away from each other andbias the pistons 152, 154 rearward. Incidentally, a rearward movement ofthe first pressurizing piston 152 is limited by that the rear endportion comes into abutting contact with a front end face of the thirdhousing member 164. The input piston 156 has a shape roughly like acylinder and is located in the rear side chamber R2. Specifically, theinput piston 156 is fitted, behind the extension portion 182 of thefirst pressurizing piston 152, in the rear small-diameter portion 172 ofthe second housing member 162 with seals.

In the master cylinder device 50 constructed thus, between the main bodyportion 180 of the first pressurizing portion 152 and the third housingmember 164, there is defined a fluid chamber R5 into which the brakefluid from the high pressure source device 58 is inputted. This fluidchamber R5 is referred to as an “input chamber”, where appropriate. Itis noted that the input chamber R5 is illustrated in an almost squeezedstate in FIG. 2. Additionally, between an inner circumferential face ofthe rear large-diameter portion 168 of the first housing member 160 infront of the flange 184 and an outer circumferential face of the mainbody portion 180 of the first pressurizing piston 152, there is definedan annular fluid chamber R6 opposing the input chamber R5 with theflange 184 being interposed between the annular fluid chamber R6 and theinput chamber R5. Hereinafter, this annular fluid chamber is referred toas an “opposing chamber”, where appropriate. Between a rear end face ofthe extension portion 182 of the first pressurizing piston 152 and afront end face of the input piston 152, there is provided a space havinga certain size in no brake operation. In a space around the extensionportion 182 including the above space, there is defined an inter-pistonchamber R8. Additionally, in the first pressurizing piston 152, apressurized area on which a pressure of a brake fluid in theinter-piston chamber R8 acts to generate a forward bias force in thefirst pressurizing piston 152, namely, an area of the rear end face ofthe extension portion 182, and a pressurized area on which a pressure ofa brake fluid in the opposing chamber R6 acts to generate a rearwardbias force in the first pressurizing piston 152, namely, an area of thefront end face of the flange 184 are equal.

In the master cylinder device 50 in which each of the chambers isdefined thus, the input chamber R5 is defined by that the firstpressurizing piston 152 contacts with an inner circumferential face ofthe rear large-diameter portion 168 of the first housing member 160 viaa seal 194 embedded in an outer circumferential face of the flange 184and contacts with an inner circumferential face defining the throughhole 178 of the third housing member 164 via a seal 196 embedded in theinner circumferential face defining the through hole 178. By the way,the input piston 156 slidably contacts with an inner circumferentialface of the second housing member 162, and seals 198, 200 are embeddedin an outer circumferential face of the input piston 156. It is notedthat a high-pressure seal is employed as each of the seals 194, 196 butnot employed as each of the seals 198, 200.

A front end portion of the operation rod 72 is connected to a rear endportion of the input piston 156 so as to transmit, to the input piston156, the operation force applied to the brake pedal 70 and so as to movethe input piston 156 forward and rearward in accordance with theoperation amount of the brake pedal 70. Incidentally, the rearwardmovement of the input piston 156 is limited by that it is stopped by arear end portion of the second housing member 162. In addition, a springseat 202 shaped like a disc is fixed to the operation rod 72, and acompression coil spring (hereinafter, referred to as a “return spring”,where appropriate) 204 is disposed between a spring seat 202 and thesecond housing member 162. The return spring 204 biases the operationrod 72 rearward. Incidentally, a boot 206 is bridged between the springseat 202 and the housing 150, whereby a rear side portion of the mastercylinder device 50 is protected from dust.

The first pressurizing chamber R3 communicates, through a communicationhole 210 provided in the first housing member 160, with the fluidpassage 80 connected to the antilock device 54, and can communicate,through a communication hole 212 provided in the first pressurizingpiston 152 and a communication hole 214 provided in the first housingmember 160, with the reservoir 62. On the other hand, the secondpressurizing chamber R4 communicates, through a communication hole 216provided in the first housing member 160, with the fluid passage 82connected to the antilock device 54, and can communicate, through acommunication hole 218 provided in the second pressurizing piston 154and a communication hole 220 provided in the first housing member 160,with the reservoir 62.

In the first housing member 160, there is provided a communication hole222 whose one end is open to the opposing chamber R6 and whose other endis open to the exterior. In addition, in the first housing member 160,there is provided a communication hole 224 whose one end is open to theinput chamber R5, and, in the second housing member 162, there isprovided a communication hole 226 whose one end is open so as to facethe other end of the communication hole 224 and whose other end is opento the exterior. That is, the input chamber R5 communicates with theexterior through the communication holes 224, 226. Moreover, in thefirst housing member 160, there is provided a communication hole 228whose one end is open to the inter-piston chamber R8 and whose other endis open to the exterior.

In the master cylinder device 50 in which the communication holes areformed thus, to the communication hole 226, an input pressure passage230 whose one end is connected to the pressure-intensifying/reducingdevice 60, specifically, the third fluid chamber 134 of the pressureadjusting valve device 100 is connected at the other end thereof.Therefore, the brake fluid whose pressure is adjusted by the pressureadjusting valve device 100 is inputted into the input chamber R5. Inaddition, on the input pressure passage 230, there is provided an inputpressure sensor [Pi] 232 for detecting a pressure of a brake fluid inthe input chamber R5.

Moreover, one end of an external communication passage 234 is connectedto the communication hole 222, and the other end thereof is connected tothe communication hole 228. Therefore, in the master cylinder device 50,the communication holes 222, 228, and the external communication passage234 constitute an inter-chamber communication passage which allows acommunication between the opposing chamber R6 and the inter-pistonchamber R8. Further, a low pressure passage 236 communicating with thereservoir 62 being a low pressure source diverges from the externalcommunication passage 234, and an electromagnetic open/close valve 238is provided on the low pressure passage 236. Therefore, the opposingchamber R6 and the inter-piston chamber R8 can communicate with thereservoir 62, thus a mechanism including the open/close valve 238, theexternal communication passage 234, and the low pressure passage 236constitutes a low-pressure-source communication mechanism for theopposing and inter-piston chambers which allows the opposing chamber R6and the inter-piston chamber R8 to communicate with the reservoir 62.Incidentally, the open/close valve 238 is a normally-opened valve whichopens in a de-energized state.

In the low pressure passage 236, there is provided a reaction forcegenerating device 250 into/from which the brake fluid flows from/intothe master cylinder device 50. FIG. 4 is a cross-sectional view of thereaction force generating device 250. The reaction force generatingdevice 250 includes a housing 252 being a casing, and a piston 254 and acompression coil spring 256 which are disposed in the housing 252. Thehousing 252 has a hollow cylindrical shape whose both ends are closed.The piston 254 has a disk shape and is disposed so as to be able toslidably contact with an inner circumferential face of the housing 252.The spring 256 is supported at one end thereof by an inner bottom faceof the housing 252 and at the other end thereof by an end face of thepiston 254. Therefore, the piston 254 is elastically supported by thehousing 252 owing to the spring 256. In an interior of the housing 252,there is defined a fluid storage chamber R9 by the other end face of thepiston 254 and the housing 252. Additionally, in the housing 252, thereis provided a communication hole 228 whose one end is open to the fluidstorage chamber R9. To the other end of the communication hole 228, afluid passage diverging from the low pressure passage 236 at between theend thereof connected to the external communication passage 234 and theopen/close valve 238 is connected. Therefore, the fluid storage chamberR9 communicates with the opposing chamber R6 and the inter-pistonchamber R8. Accordingly, as a total volume of the opposing chamber R6and the inter-piston chamber R8 decreases, a volume of the fluid storagechamber R9 increases according to the decrease and the spring 256generates an elastic reaction force according to the amount of theincrease. That is, a mechanism including the spring 256 is anelastic-reaction-force applying mechanism for the fluid storage chamberwhich applies an elastic reaction force with a magnitude according tothe amount of the increase of the volume of the fluid storage chamber R9to a brake fluid in the fluid storage chamber R9.

By the way, the reaction force generating device 250 employed in themaster cylinder device 50 may be a so-called diaphragm type. That is, areaction force generating device in which the fluid storage chamber R9is defined by a diaphragm as an alternative of the piston 254 and thebrake fluid is pressurized by a pressure of a gas in a gas chamberprovided with the diaphragm being interposed between the fluid storagechamber R9 and the gas chamber may be employed.

<<Actuation of Hydraulic Brake System>>

Actuation of the hydraulic brake system 40 will be described below. In anormal condition, that is, in a condition in which the hydraulic brakesystem 40 can be actuated normally, as described above, when the targetbrake force becomes larger than the regenerative brake force by theregenerative brake, a surplus of the target brake force being above theregenerative brake force is determined as the target hydraulic brakeforce. In the pressure-intensifying/reducing device 60, the pressure ofthe brake fluid from the high pressure source device 58 is adjustedaccording to the target hydraulic brake force, and then thepressure-adjusted brake fluid is introduced into the input chamber R5.The first pressurizing piston 152 moves forward depending on thepressure of the brake fluid in the input chamber R5 so as to pressurizethe brake fluid in the first pressurizing chamber R3. The secondpressurizing piston 154 also moves forward depending on the pressure ofthe brake fluid in the first pressurizing chamber R3 so as to pressurizethe brake fluid in the second pressurizing chamber R4. The pressurizedbrake fluid is supplied via the antilock device 54 to each of the brakedevices 56, which then generates the hydraulic brake force.Incidentally, the brake ECU 38 monitors a detected value of the inputpressure sensor 232, and the pressure-intensifying/reducing device 60 iscontrolled so that the input pressure is controlled to be a pressureaccording to the target hydraulic brake force.

The pressure of the brake fluid in the opposing chamber R6 acts on thefront end face of the flange 184, therefore the rearward bias force isapplied to the first pressurizing piston 152. Additionally, the pressureof the brake fluid in the inter-piston chamber R8 acts on the rear endface of the extension portion 182 of the first pressurizing piston 152,therefore the forward bias force is applied to the first pressurizingpiston 152. As described above, in the first pressurizing piston 152,since the pressurized area on which the pressure of the brake fluid inthe opposing chamber R6 acts and the pressurized area on which thepressure of a brake fluid in the inter-piston chamber R8 acts are equal,the forward bias force and the rearward bias force become equal.Consequently, the first pressurizing piston 152 is moved depending onnot the pressure of the brake fluid in the opposing chamber R6 and thepressure of the brake fluid in the inter-piston chamber R8 but thepressure of the brake fluid in the input chamber R5.

In the first pressurizing piston 152, as described above, the twopressurized areas are equal. Therefore, a volume decrease amount of oneof the opposing chamber R6 and the inter-piston chamber R8 and a volumeincrease amount of the other of them which associate with a movement ofthe first pressurizing piston 152 become equal. As a result, when thefirst pressurizing piston 152 moves, the brake fluid flows between theopposing chamber R6 and the inter-piston chamber R8 while each volume ofthe chambers changes. That is, even though the first pressurizing piston152 moves, the total volume of the opposing chamber R6 and theinter-piston chamber R8 does not change, and each of the pressures ofthe brake fluids in the opposing chamber R6, the inter-piston chamberR8, and the fluid storage chamber R9 does not change. Therefore, evenwhen the first pressurizing piston 152 moves depending on the pressureof the brake fluid in the input chamber R5, this movement does not causeany movement of the input piston 156. That is, the master cylinderdevice 50 is configured such that the first pressurizing piston 152 andthe input piston 156 can move independently from each other in thenormal condition. Accordingly, in the master cylinder device 50, a“high-pressure-source-pressure dependent pressurizing state”, that is, astate in which the brake fluid supplied to the brake devices 56 can bepressurized depending on the pressure of the brake fluid introduced fromthe high pressure source device 58 is realized in the normal condition.So to speak, in the master cylinder device 50, thehigh-pressure-source-pressure dependent pressurizing state is realizedwith the input piston 156 being able to move freely relative to thefirst pressurizing piston 152.

Additionally, in the normal condition, when the input piston 156 movesforward relative to the first pressurizing piston 152 in accordance withan increase of the operation amount of the brake pedal 70 by the driver,the brake fluid in the inter-piston chamber R8 flows out, thus the totalvolume of the opposing chamber R6 and the inter-piston chamber R8decreases. In the normal condition, since the open/close valve 238 isenergized to be closed, the above outflowed brake fluid flows into thefluid storage chamber R9 of the reaction force generating device 250,thus the volume of the fluid storage chamber R9 increases. Therefore,the elastic reaction force of the spring 256 increases, each of thepressures of the brake fluids in the opposing chamber R6, theinter-piston chamber R8, and the fluid storage chamber R9 increases.

Additionally, the above pressure of the brake fluid in the inter-pistonchamber R8 acts on the front end face of the input piston 156, thereforea rearward bias force is applied to the input piston 156. Since thisrearward bias force is transmitted via the input piston 156 to the brakepedal 70, the driver can feel the bias force as the operation reactionforce against a brake operation by the driver. In addition, since thepressure of the brake fluid in the inter-piston chamber R8, as describedabove, increases according to the forward movement of the input piston156, the driver can feel that the operation reaction force increasesaccording to the increase of the brake operation amount by the driverirrespective of the pressures of the brake fluids in the pressurizingchambers R3, R4, namely, the actual hydraulic brake force. That is, itis considered that a stroke simulator which allows a brake operation bythe driver while generating the reaction force in accordance with theoperation is constructed.

When, in realization of high-pressure-source-pressure dependentpressurizing state, a large hydraulic brake force is required, such asan emergency brake (hereinafter, referred to as a“large-brake-force-required condition”, where appropriate), theopen/close valve 238 is de-energized to be opened in the hydraulic brakesystem 40. Consequently, the opposing chamber R6 and the inter-pistonchamber R8 communicate with the reservoir 62 via the externalcommunication passage 234 and the low pressure passage 236, and thefluid storage chamber R9 of the reaction force generating device 250also communicates with the reservoir 62. Therefore, the input piston 156can move forward with the brake fluids in the inter-piston chamber R8and the opposing chamber R6 being flowed into the reservoir 62, therebycoming into an abutting contact with the extension portion 182 of thefirst pressurizing piston 152. Upon this forward movement, since theoperation reaction force by the reaction force generating device 250does not generate, it is allowed that the input piston 156 easily comesinto an abutting contact with the first pressurizing piston 152.Therefore, since the brake operation force by the driver is transmittedfrom the input piston 156 to the first pressurizing piston 152, itbecomes possible to pressurize the brake fluids in the pressurizingchambers R3, R4 depending on not only the pressure of the brake fluidfrom the high pressure source device 58 but also the operation force.Accordingly, in the master cylinder device 50, an“operation-force/high-pressure-source-pressure dependent pressurizingstate”, that is, a state in which the brake fluid supplied to the brakedevices 56 can be pressurized depending on not only the pressure of thebrake fluid introduced from the high pressure source device 58 but alsothe operation force is realized in the large-brake-force-requiredcondition. Therefore, the first pressurizing piston 156 can beconsidered a pressure receiving piston which pressurizes the brake fluidto be supplied to the brake devices 56 by receiving the operation forceand the pressure of the brake fluid supplied to the input chamber R5.Incidentally, in the operation-force/high-pressure-source-pressuredependent pressurizing state, since the pressure of the brake fluids inthe pressurizing chambers R3, R4 is transmitted to the input piston 310,the driver can feel the rearward bias force generated by the pressure asthe operation reaction force.

By the way, a determination whether the hydraulic brake system 40 is inthe above large-brake-force-required condition or not is carried out bya comparison of the above target hydraulic brake force with the maximumhydraulic brake force in the high-pressure-source-pressure dependentpressurizing state, that is, a hydraulic brake force in a case in whichthe input pressure is fairly equal to the high-pressure-source pressure.That is, when the target hydraulic brake force becomes larger than themaximum hydraulic brake force, a switch from thehigh-pressure-source-pressure dependent pressurizing state to theoperation-force/high-pressure-source-pressure dependent pressurizingstate is performed. Therefore, in the hydraulic brake system 40, thebrake ECU 38 determines whether the large hydraulic brake force isrequired or not, depending on the detected value of thehigh-pressure-source pressure 96 and the detected value of the inputpressure sensor 232. Additionally, in consideration of a margin forperforming the switch smoothly, the brake ECU 38 is configured to outputa command for opening the open/close valve 238 when the input pressurebecomes higher than a set pressure determined to be slightly lower thanthe high-pressure-source pressure. As for a switch from theoperation-force/high-pressure-source-pressure dependent pressurizingstate to the high-pressure-source-pressure dependent pressurizing state,the brake ECU 38 is configured to output a command for closing theopen/close valve 238 when the input pressure becomes lower than the setpressure.

Incidentally, the hydraulic brake system 40 may utilize, as a parameterfor determining whether the large hydraulic brake force is required ornot, the master pressure, the brake operation amount, the brakeoperation force, a vehicle speed, or so on. That is, when the masterpressure is high or the brake operation force is large, it is possibleto determine, based on the fact, that the required hydraulic brake forceis large. In the case of the brake operation amount, it is possible tocalculate, by utilizing its variation, an operation speed of the brakepedal 70, and then to determine an emergency brake etc. In the case ofthe vehicle speed, it is possible to calculate, by utilizing itsvariation, a deceleration of the vehicle, and then to determine anemergency brake etc.

Next, it will be described how the master cylinder device 50 is actuatedin a condition in which electric power is not supplied to the hydraulicbrake system 40 due to an electric failure. In the electric failurecondition, the hydraulic pump 90 of the high pressure source device 60cannot work and the pressure-intensifying linear valve 102 and thepressure-reducing linear valve 104 cannot be activated. Additionally,the open/close valve 238 is de-energized to be opened. Therefore, as inthe operation-force/high-pressure-source-pressure dependent pressurizingstate, the first pressurizing piston 152 can move forward depending onthe operation force. Accordingly, in the master cylinder device 50, an“operation-force dependent pressurizing state”, that is, a state inwhich the brake fluid supplied to the brake devices 56 can bepressurized depending on only the operation force is realized.

It is noted that the pressure adjusting valve device 100 can be stillactivated by using the above pilot-pressure-dependent pressure reducingmechanism. Therefore, when the pressure-intensified brake fluid isstored in the accumulator 92 immediately after an occurrence of anelectric failure, the pressure adjusting valve device 100 can adjust thepressure of the brake fluid, and then the pressure-adjusted brake fluidis introduced into the input chamber R5. Accordingly, even in theelectric failure condition, theoperation-force/high-pressure-source-pressure dependent pressurizingstate can be realized, and the brake fluids in the pressurizing chambersR3, R4 can be pressurized depending on not only the operation force.Therefore, in the pressure adjusting valve device 100, where a mechanismincluding the pressure-intensifying linear valve 102 and thepressure-reducing linear valve 104 is considered to be a main pressurereducing mechanism of the pressure adjusting valve device 100, that is,a main pressure reducing mechanism for reducing the pressure of thebrake fluid supplied from the high pressure source device 58, thepilot-pressure-dependent pressure reducing mechanism can be consideredto be an auxiliary pressure reducing mechanism.

In the master cylinder device 50, the input piston 156 is not fitted tothe first pressurizing piston 152 with any seal. Therefore, even whenthe first pressurizing piston 152 is moved by the pressure of the brakefluid in the input chamber R5, no force resulting from any frictionforce of any seal acts on the input piston 156. Therefore, since amovement of the first pressurizing piston 152 does not pull the inputpiston 156 and the brake pedal 70 and thus does not cause the inputpiston 156 and the brake pedal 70 to be moved, operational feeling in abrake operation is excellent.

In addition, as described above, a high-pressure seal is employed aseach of the seals 194, 196, whereby the master cylinder device 50 isconstructed not to cause a leak of the brake fluid in the input chamberR5 even in a condition in which the pressure of the brake fluid becomesconsiderably high in the large-brake-force-required condition etc.Therefore, the seals 194, 196 result in generating a comparatively largefriction force upon a movement of the first pressurizing piston 152. Onthe other hand, since both of the seals 198, 200 between the inputpiston 156 and the housing 150 are not high-pressure seals, each of themcauses a comparatively small friction force upon a movement of the inputpiston 156. Therefore, in the master cylinder device 50, a resistanceupon a movement of the input piston 156 is comparatively small, wherebyoperational feeling in a brake operation is excellent. Especially in theoperation-force dependent pressurizing state, it is possible to provideexcellent operational feeling.

Second Embodiment

FIG. 5 schematically represents a hydraulic brake system 300 of thesecond embodiment. The hydraulic brake system 300 has a master cylinderdevice 302. The hydraulic brake system 300 generally has the samestructure as the hydraulic brake system 40 of the first embodiment. Inthe following description, with consideration for abbreviating theexplanation, different construction and actuation from the hydraulicbrake system 40 of the first embodiment will be described but the sameconstruction and actuation as the hydraulic brake system 40 of the firstembodiment are omitted.

<<Structure of Master Cylinder Device>>

The master cylinder device 302 is categorized into the Input Piston FreeType Master Cylinder Device, and has a housing 304 being a casing, afirst pressurizing piston 306 and a second pressurizing piston 308 whichpressurize the brake fluid to be supplied to the brake devices 56, andan input piston 310 to which an operation of the driver is inputted viathe operation device 52.

The housing 304 mainly includes four members, specifically, a firsthousing member 312, a second housing member 314, a third housing member316, and a fourth housing member 318, and has a roughly hollowcylindrical shape whose front end is closed. Among these housingmembers, the second housing member 314 has a roughly hollow cylindricalshape, and is sectioned into three portions having mutually differentinner diameters, specifically, a front large-diameter portion 320arranged in a front side and having a large inner diameter, a rearsmall-diameter portion 322 arranged in a rear side and having a smallinner diameter, and an intermediate portion 324 arranged between theabove two portions and having an inner diameter of a medium size betweenthe above two inner diameters. In the intermediate portion 324 of thesecond housing member 314, there is fitted a third housing member 316having a disk shape and provided with a through hole 326 in the centerthereof. An interior of the housing 304 constructed thus is separated bythe third housing member 316 to define a front side chamber R11 locatedin a front side and a rear side chamber R12 located in a rear side. Thatis, the third housing member 316 serves as a partition portionseparating the interior of the housing 304, and the through hole 326serves as an opening of the partition portion.

The second pressurizing piston 308 has a hollow cylindrical shape whoserear end portion is closed, and is slidably fitted with seals in thefirst housing member 312 in the front side chamber R11. The firstpressurizing piston 306 includes a main body portion 330 located in thefront side chamber R11 and having a hollow cylindrical shape whose rearend portion is closed, and an extension portion 332 fixed in a rear endportion of the main body portion 330 and extending through the throughhole 326 into the rear side chamber R12. Additionally, on an outerperiphery of a bottom portion of the main body portion 330, there isprovided a flange 334. The first pressurizing piston 306 is fitted inthe housing 304 with seals such that a front portion of the main bodyportion 330 slidably contacts with the first housing member 312, theflange 334 slidably contacts with the rear large-diameter portion 320 ofthe second housing member 312, and the extension portion 332 slidablycontacts with the through hole 326 of the third housing member 316.

The input piston 310 is disposed in the rear side chamber R12 and isfitted, behind the extension portion 332 of the first pressurizingpiston 306, in the rear small-diameter portion 322 of the second housingmember 314. The input piston 310 includes a base end portion 336 towhich the operation rod 72 is connected, a guide portion 338 having ahollow cylindrical shape and extending forward from the base end portion336, and a movable portion 340 slidably contacting with an inside of theguide 338. In the input piston 310, a rearward movement of the movableportion 340 relative to the base end portion 336, in other words, ashrink of the input piston 310 is allowed. Additionally, between thebase end portion 336 and the movable portion 340, there is disposed acompression coil spring 342 which generates an elastic reaction forcefor separating the base end portion 336 and the movable portion 340 fromeach other. Incidentally, an inner flange is provided on an innerperiphery of a front end portion of the guide portion 338, and the innerflange prevents the movable portion 340 from coming out forward from theguide portion 338. An inner diameter of the guide portion 338 is largerthan an outer diameter of the extension portion 332 of the firstpressurizing piston 306, and the first pressurizing piston 306 and theinput piston 310 are disposed such that a rear end of the extensionportion 332 is inserted into the inside of the guide portion 338. Thatis, a part of the first pressurizing piston 306 and the part of theinput piston 310 overlap with each other in the front-back direction.

In the master cylinder device 302 constructed thus, between the mainbody portion 330 of the first pressurizing portion 306 and the thirdhousing member 316, there is defined a fluid chamber R15 into which thebrake fluid from the high pressure source device 58 is inputted. Thisfluid chamber R15 is referred to as an “input chamber”, whereappropriate. Additionally, between an inner circumferential face of thesecond housing member 314 in front of the flange 334 and an outercircumferential face of the first pressurizing piston 306, there isdefined an annular fluid chamber R16 opposing the input chamber R15 withthe flange 334 being interposed between the opposing chamber R16 and theinput chamber R15. Hereinafter, this chamber is referred to as an“opposing chamber”, where appropriate. Moreover, inside the input piston310, there is defined a fluid chamber (hereinafter, referred to as an“internal chamber”, where appropriate) R17 between the base end portion336 and the movable portion 340. Furthermore, between a rear end face ofthe extension portion 332 of the first pressurizing piston 306 and afront end face of the movable portion 340 of the input piston 310, thereis provided a clearance which is small in no brake operation. In a spacearound the extension portion 332 including the above clearance, there isdefined an inter-piston chamber R18. Additionally, in the firstpressurizing piston 306, a pressurized area on which a pressure of abrake fluid in the inter-piston chamber R18 acts, namely, an area of therear end face of the extension portion 332, and a pressurized area onwhich a pressure of a brake fluid in the opposing chamber R16 acts,namely, an area of the front end face of the flange 334 are equal.

In the master cylinder device 302 in which each of the chambers isdefined thus, the input chamber R15 is defined by that the firstpressurizing piston 306 contacts with the inner circumferential face ofthe second housing member 314 via a seal 344 embedded in an outercircumferential face of the flange 334 and contacts with an innercircumferential face defining the through hole 326 of the third housingmember 316 via a seal 346 embedded in the inner circumferential facedefining the through hole 326. In addition, the input piston 310slidably contacts with the inner circumferential face of the secondhousing member 314. Therefore, a seal 348 is embedded in an outercircumferential face of the base end portion 336, and a seal 350 isembedded in an outer circumferential face of the front end of the guideportion 338. It is noted that a high-pressure seal is employed as eachof the seals 344, 346 but not employed as each of the seals 348, 350.

In the first housing member 312, there is provided a communication hole360 whose one end is open to the opposing chamber R16. In the secondhousing member 314, there is provided a communication hole 362 whose oneend is open so as to face the other end of the communication hole 360,and, in the fourth housing member 318, there is provided a communicationhole 364 whose one end is open so as to face the other end of thecommunication hole 362 and whose other end is open to the exterior. Thatis, the opposing chamber R16 communicates with the exterior through thecommunication holes 360, 362, 364. In addition, in the second housingmember 314, there is provided a communication hole 366 whose one end isopen to the input chamber R15, and, in the fourth housing member 318,there is provided a communication hole 368 whose one end is open so asto face the other end of the communication hole 366 and whose other endis open to the exterior. That is, the input chamber R15 communicateswith the exterior through the communication holes 366, 368.

Since an outer diameter of a part of the guide portion 338 of the inputpiston 310 is slightly smaller than an inner diameter of the rearsmall-diameter portion 322 of the second housing member 314, a fluidpassage 370 is formed between the guide portion 338 and the rearsmall-diameter portion 322. In addition, between an outercircumferential face of the second housing member 314 and an innercircumferential face of the fourth housing member 318, there is formed afluid passage 372 since an outer diameter of the second housing member314 and an inner diameter of the fourth housing member 318 are differentfrom each other. In the input piston 310, there is provided acommunication hole 374 whose one end is open to the internal chamber R17and whose other end is open to the fluid passage 370. In the secondhousing member 314, there is provided a communication hole 376 whose oneend is open to the fluid passage 370 and whose other end is open to thefluid passage 372. Moreover, in the fourth housing member 318, there isprovided a communication hole 378 whose one end is open to the fluidpassage 372 and whose other end is open to the exterior. That is, theinternal chamber R17 communicates with the exterior through thecommunication hole 374, the fluid passage 370, the communication hole376, the fluid passage 372, and the communication hole 378.

Additionally, inside the first pressurizing piston 306, there is formedan internal communication passage 380 whose one end is open on the rearend face of the extension portion 332 and whose other end is open infront of the flange 334 of the main body portion 330. Therefore, in themaster cylinder device 302, the internal communication passage 380constitutes an inter-chamber communication passage which allows acommunication between the opposing chamber R16 and the inter-pistonchamber R18. Therefore, the inter-piston chamber R18 also communicateswith the exterior through the internal communication passage 380, theopposing chamber R16, the communication holes 360, 362, 364.

In the master cylinder device 302 formed thus, to the communication hole368, an input pressure passage 230 whose one end is connected to thethird fluid chamber 134 of the pressure adjusting valve device 100 isconnected at the other end thereof. Additionally, to the communicationhole 364, one end of the external communication passage 382communicating with the reservoir 62 is connected, and an electromagneticopen/close valve 384 which is a normally-opened valve is provided on theexternal communication passage 382. Therefore, a mechanism including theexternal communication passage 382 and the open/close valve 384constitutes a low-pressure-source communication mechanism for theopposing and inter-piston chambers which allows the opposing chamber R6and the inter-piston chamber R8 to communicate with the reservoir 62.Moreover, in the external communication passage 382, there is provided acheck valve 386 in parallel with the open/close valve 384 in order thateach of the pressures of the brake fluids in the opposing chamber R16and the inter-piston chamber R18 does not become lower than a pressureof the brake fluid in the reservoir 62. In the low pressure passage 382,a reaction force generating device 250 into/from which the brake fluidflows from/into the master cylinder device 302 is provided between theend connecting to the communication hole 364 and the open/close valve384.

To the communication hole 378, one end of a low pressure passage 388communicating with the reservoir 62 is connected, and an electromagneticopen/close valve 390 which is a normally-closed valve is provided on thelow pressure passage 388. Therefore, the internal chamber R17 cancommunicate with the reservoir 62. Additionally, when the open/closevalve 390 is closed, the internal chamber R17 is hermetically closed.That is, a mechanism including the low pressure passage 388 and theopen/close valve 390 can be considered to be an input-piston-shrinkprohibiting mechanism which prohibits the shrink of the input piston 310by hermetically closing the internal chamber R17.

<<Actuation of Hydraulic Brake System>>

Actuation of the hydraulic brake system 300 will be described below. Inthe normal condition, that is, in a condition in which the hydraulicbrake system 300 can be actuated normally, the open/close valve 384 isenergized to be closed and the open/close valve 390 is energized to beopened. In this state, the brake fluid whose pressure is adjustedaccording to the target hydraulic brake force is inputted into the inputchamber R15. The first pressurizing piston 306 moves forward dependingon the pressure of the brake fluid in the input chamber R15 so as topressurize the brake fluid in the first pressurizing chamber R3 and thenpressurize the brake fluid in the second pressurizing chamber R4.Additionally, in the normal condition, when the input piston 310 movesforward relative to the first pressurizing piston 306 in accordance withan increase of the operation amount, the brake fluid in the inter-pistonchamber R18 flows out via the opposing chamber R16, thus a total volumeof the opposing chamber R16 and the inter-piston chamber R18 decreases.The outflowed brake fluid flows into the fluid storage chamber R9 of thereaction force generating device 250, and then each of the pressures ofthe brake fluids in the opposing chamber R16, the inter-piston chamberR18, and the fluid storage chamber R9 increases.

As described above, in the first pressurizing piston 306, since thepressurized area on which the pressure of the brake fluid in theopposing chamber R16 acts and the pressurized area on which the pressureof a brake fluid in the inter-piston chamber R18 acts are equal, thefirst pressurizing piston 306 is moved depending on not the pressure ofthe brake fluid in the opposing chamber R16 and the pressure of thebrake fluid in the inter-piston chamber R18 but the pressure of thebrake fluid from the high pressure source device 58. Additionally, amovement of the first pressurizing piston 306 does not cause anymovement of the input piston 310. Accordingly, in the master cylinderdevice 302, the high-pressure-source-pressure dependent pressurizingstate is realized in the normal condition.

Additionally, in the input piston 310 in the normal condition, the baseend portion 336 and the guide portion 338 move forward relative to themovable portion 340 by the operation force and the pressure of the brakefluid in the inter-piston chamber R18. In other words, the input piston310 shrinks with the brake fluid in the internal chamber R17 beingflowed out, thus the spring 342 generates an elastic reaction forceaccording to an amount of the shrink. That is, a mechanism including thespring 342 is an elastic-reaction-force applying mechanism for the inputpiston which applies the elastic reaction force with a magnitudeaccording to the amount of the shrink to the base end portion 336 andthe movable portion 340. Therefore, when the input piston 310 shrinks, arearward bias force acts on the base end portion 336 to which the brakepedal 70 is connected, whereby the driver can feel the bias force as anoperation reaction force against a brake operation by the driver. Also,the above described operation reaction force by theelastic-reaction-force applying mechanism for the fluid storage chamber,that is, the spring 256 of the reaction force generating device 250 actson the base end portion 336. Consequently, it is possible to say thatthe master cylinder device 302 have two elastic-reaction-force-applyingmechanisms, that is, the elastic-reaction-force applying mechanism forthe input piston and the elastic-reaction-force applying mechanism forthe fluid storage chamber.

In the master cylinder device 302, the base end portion 336 of the inputpiston 310 comes into abutting contact with the movable portion 340 at acertain brake operation amount. That is, the input piston 310 becomes tobe incapable of shrinking, therefore the operation reaction force isgenerated only by the elastic-reaction-force applying mechanism for thefluid storage chamber in a brake operation exceeding the certain brakeoperation amount. Therefore, the spring constant of the spring 342 ofthe elastic-reaction-force applying mechanism for the input piston isconsiderably smaller than the spring constant of the spring 256 of theelastic-reaction-force applying mechanism for the fluid storage chamber.Since the two elastic-reaction-force-applying mechanisms are constructedthus, a ratio of the operation force to the operation amount iscomparatively small from a start of a brake operation to the certainbrake operation amount and becomes comparatively large in a brakeoperation exceeding the certain brake operation amount. That is, themaster cylinder device 302 is configured such that, as the operationamount of the brake pedal 70 increases, a ratio of increase of theoperation reaction force increases owing to the twoelastic-reaction-force-applying mechanisms.

In the large-brake-force-required condition, the open/close valve 384 isde-energized to be opened in the hydraulic brake system 300. Therefore,the input piston 310 moves forward with the brake fluids in theinter-piston chamber R18 and the opposing chamber R16 being flowed intothe reservoir 62. Therefore, when the movable portion 340 of the inputpiston 310 comes into an abutting contact with the extension portion 332of the first pressurizing piston 306, the first pressurizing piston 306can be moved forward by the operation force. That is, it is possible topressurize the brake fluids in the pressurizing chambers R3, R4depending on not only the pressure of the brake fluid from the highpressure source device 58 but also the operation force. Accordingly, inthe master cylinder device 302, theoperation-force/high-pressure-source-pressure dependent pressurizingstate is realized in the large-brake-force-required condition.Accordingly, the first pressurizing piston 306 can be considered apressure receiving piston which pressurizes the brake fluid to besupplied to the brake devices 56 by receiving the operation force or thepressure of the brake fluid supplied to the input chamber R15. In thelarge-brake-force-required condition, the open/close valve 390 is alsode-energized to be closed, thereby prohibiting the shrink of the inputpiston 310. Therefore, the brake operation force by the driver istransmitted to the first pressurizing piston 306 without shrinking theinput piston 310, that is, without generating an ineffective brakeoperation amount. Incidentally, in theoperation-force/high-pressure-source-pressure dependent pressurizingstate, since the pressure of the brake fluids in the pressurizingchambers R3, R4 is transmitted to the input piston 310, the driver canfeel the rearward bias force generated by the pressure as the operationreaction force.

In a condition in which electric power is not supplied to the hydraulicbrake system 300 due to an electric failure, the open/close valve 384 isde-energized to be opened and the open/close valve 390 is de-energizedto be closed. Therefore, as in theoperation-force/high-pressure-source-pressure dependent pressurizingstate, the first pressurizing piston 306 can move forward depending onthe operation force. That is, in the master cylinder device 302, theoperation-force dependent pressurizing state is realized.

In the master cylinder device 302, the pressure adjusting valve device100 may be activated by utilizing, as the pilot pressure, not the masterpressure but the pressure of the brake fluid in the internal chamberR17. In this case, the first fluid chamber 130 may be connected not tothe fluid passage diverging from the fluid passage 80 but to a fluidpassage diverging from between the communication hole 378 and theopen/close valve 390 on the low pressure passage 388. As describedabove, the open/close valve 390 is de-energized to be closed, wherebythe internal chamber R17 is hermetically closed in the operation-forcedependent pressurizing state. Therefore, in the operation-forcedependent pressurizing state, the pressure of the brake fluid in thefirst pressurizing chamber R3 is transmitted to the input piston 310 viathe first pressurizing piston 306, whereby a force by the pressure ofthe brake fluid in the internal chamber R17 has a magnitude to be equalto a force by the pressure of the brake fluid in the first pressurizingchamber R3. That is, the pressure of the brake fluid in the internalchamber R17 is a pressure indicating the master pressure, therefore thepressure adjusting valve device 100 is activated while indirectlyutilizing the master pressure as the pilot pressure.

In the master cylinder device 302, the input piston 310 is not fitted tothe first pressurizing piston 306 with any seal. Therefore, even whenthe first pressurizing piston 306 is moved by the pressure of the brakefluid in the input chamber R15, no force resulting from any frictionforce of any seal acts on the input piston 310. In addition, each of thehigh-pressure seals 344, 346 between the first pressurizing piston 306and the housing 304 causes a comparatively large friction force upon amovement of the first pressurizing piston 306, whereas each of the seals348, 350 between the input piston 310 and the housing 304 causes acomparatively small friction force upon a movement of the input piston310. Therefore, in the master cylinder device 302, operational feelingin a brake operation is excellent. Especially in the operation-forcedependent pressurizing state, it is possible to provide excellentoperational feeling.

Third Embodiment

FIG. 6 schematically represents a hydraulic brake system 400 of thethird embodiment. The hydraulic brake system 400 has a master cylinderdevice 402. The hydraulic brake system 400 generally has the samestructure as each of the hydraulic brake systems of the first and thesecond embodiments. In the following description, with consideration forabbreviating the explanation, different construction and actuation fromthe hydraulic brake systems will be described but the same constructionand actuation as the hydraulic brake systems are omitted.

<<Structure of Master Cylinder Device>>

The master cylinder device 402 is categorized into the Input Piston FreeType Master Cylinder, and has a housing 404 being a casing, a firstpressurizing piston 406 and a second pressurizing piston 408 whichpressurize the brake fluid to be supplied to the brake devices 56, andan input piston 410 to which an operation of the driver is inputted viathe operation device 52.

The housing 404 mainly includes three members, specifically, a firsthousing member 412, a second housing member 414, and a third housingmember 416, and has a roughly hollow cylindrical shape whose front endis closed. Among these housing members, the third housing member 416 hasa roughly hollow cylindrical shape, and is sectioned into a front sideportion 418 arranged in a front side, a rear side portion 420 arrangedin a rear side, and an intermediate portion 422 arranged between theabove two portions and having an outer diameter larger than that of thefront side portion 418 and that of the rear side portion 420.

In the housing 404 constructed above, the intermediate portion 422 ofthe third housing member 416 serves an annular separation wall portionprojecting to the inside in a radial direction, and the front sideportion 418 serves an inner cylindrical portion extending forward froman inner periphery of the separation wall portion. In other words, inthe housing 404, a partition portion separating an interior of thehousing 404 is formed by the intermediate portion 422 and the front sideportion 418. Therefore, the interior of the housing 404 is separatedinto a front side chamber R21 including an outside space of the frontside portion 418 and a rear side chamber R22 including an inside spaceof the front side portion 418. In addition, a front end of the frontside portion 418 serves as an opening formed in the partition portion.

The second pressurizing piston 408 has a hollow cylindrical shape whoserear end portion is closed, and is slidably fitted with seals in thefirst housing member 412 in the front side chamber R21. The firstpressurizing piston 406 includes a main body portion 426 disposed in thefront side chamber R21 and having a roughly hollow cylindrical shape,and a separation wall 428 disposed approximately in the middle of themain body portion 426 in the front-back direction and separating aninterior of the first pressurizing piston 406 in the front-backdirection. Therefore, in the first pressurizing piston 406, a rearportion of the separation wall 428 serves as a cylindrical portion 430including a blind hole being open rearward. In addition, a flange 432 isformed on a rear end of the cylindrical portion 430. The firstpressurizing piston 406 formed thus is fitted with seals in the housing404 such that a front portion of the main body portion 426 slidablycontacts with the first housing member 412, the flange 432 slidablycontacts with the second housing member 414, and the cylindrical portion430 slidably contacts with the front side portion 418 of the thirdhousing member 416. That is, the first pressurizing piston 406 isdisposed such that the front side portion 418 of the third housingmember 416 is inserted in the cylindrical portion 430, in other words,such that the cylindrical portion 430 is interposed between the secondhousing member 414 and the front side portion 418 of the third housingmember 416. So to speak, the second housing member 414 can be consideredto be an outer cylindrical portion of the housing 404.

The input piston 410 includes a base end portion 434 to which theoperation rod 72 is connected, a rod portion 436 screwed in the base endportion 434 and extending forward from the base end portion 434, and amovable portion 438 slidably fitted to the rod portion 436. In the inputpiston 410, a rearward movement of the movable portion 438 relative tothe base end portion 434, in other words, a shrink of the input piston410 is allowed. Additionally, between the base end portion 434 and themovable portion 438, two compression coil springs 440, 442 each of whichgenerates an elastic reaction force for biasing the movable portion 438forward are disposed in series in the front-back direction. It is notedthat the spring constant of the spring 440 is smaller than the springconstant of the spring 442. Additionally, between the springs 440, 442,a floating seat 443 is disposed such that it is supported by them.Incidentally, an outer flange is provided on an outer periphery of afront end portion of the rod portion 436, and the outer flange preventsthe movable portion 438 from coming out forward from the rod portion436. The input piston 410 is fitted in an inside of the third housingmember 416 with a front portion of the input piston 410 being insertedin the front side portion 418 of the third housing member 416. That is,the input piston 410 is disposed such that the front side thereof islocated in the cylindrical portion 430 of the first pressurizing piston406. Accordingly, in the master cylinder device 402, since a part of thefirst pressurizing piston 406 and a part of the input piston 410 overlapwith each other in the front-back direction, the entire length of themaster cylinder device 402 is comparatively short.

In the master cylinder device 402 constructed thus, between a rear endof the main body portion 426 of the first pressurizing portion 406 andthe intermediate portion 422 of the third housing member 416, there isdefined a fluid chamber R25 into which the brake fluid from the highpressure source device 58 is inputted. This fluid chamber R25 isreferred to as an “input chamber”, where appropriate. Additionally,between an inner circumferential face of the second housing member 414in front of the flange 432 and an outer circumferential face of thefirst pressurizing piston 406, there is defined an annular fluid chamberR26 opposing the input chamber R25 with the flange 432 being interposedbetween the opposing chamber R26 and the input chamber R25. Hereinafter,this chamber is referred to as an “opposing chamber”, where appropriate.Moreover, inside the input piston 410, a fluid chamber (hereinafter,referred to as an “internal chamber”, where appropriate) R27 forallowing a shrink of the input piston 410 is defined between the baseend portion 434 and the movable portion 438. Furthermore, between abottom face of a rearward-open blind hole of the first pressurizingpiston 406 and a face of the input piston 410 which faces forward, thereis defined an inter-piston chamber R28 across which the input piston 410and the first pressurizing piston 406 face to each other. Additionally,in the first pressurizing piston 406, a pressurized area on which apressure of a brake fluid in the inter-piston chamber R28 acts, namely,an area of the bottom face of the rearward-open blind hole, and apressurized area on which a pressure of a brake fluid in the opposingchamber R26 acts, namely, an area of a front end face of the flange 432are equal.

In the master cylinder device 402 in which each of the chambers isdefined thus, the input chamber R25 is defined by that the firstpressurizing piston 406 contacts with the inner circumferential face ofthe second housing member 414 via a seal 444 embedded in an outercircumferential face of the flange 432 and contacts with an outercircumferential face of the front side portion 418 of the third housingmember 416 via a seal 446 embedded in an inner circumferential face ofthe cylindrical portion 430. In addition, the input piston 410 slidablycontacts with the inner circumferential face of the second housingmember 414. Therefore, a seal 448 is embedded in an outercircumferential face of the base end portion 434, and a seal 450 isembedded in an outer circumferential face of the movable portion 438. Itis noted that a high-pressure seal is employed as each of the seals 444,446 but not employed as each of the seals 448, 450.

In the second housing member 414, there is provided a communication hole460 whose one end is open to the opposing chamber R26. Additionally, inthe cylindrical portion 430 of the first pressurizing piston 406, thereis provided a communication hole 462 whose one end is open to theopposing chamber R26. Between the inner circumferential face of thecylindrical portion 430 of the first pressurizing piston 406 and theouter circumferential face of the front side portion 418 of the thirdhousing member 416, there is provided a clearance 464 having a certaincross section area through which the brake fluid can flow, though it ishard to be seen from the figure. Therefore, in the master cylinderdevice 402, the clearance 464 and the communication hole 460 constitutean inter-chamber communication passage which allows a communicationbetween the opposing chamber R26 and the inter-piston chamber R28.Therefore, the inter-piston chamber R28 also communicates with theexterior through the clearance 464, the communication hole 462, theopposing chamber R26, and the communication hole 460. In the secondhousing member 414, there is also provided a communication hole 466whose one end is open to the input chamber R25. In the third housingmember 416, there is provided a communication hole 468 whose one end isopen to the internal chamber R27, and, in the second housing member 414,there is provided a communication hole 470 whose one end is open so asto face the other end of the communication hole 468 and whose other endis open to the exterior. That is, the internal chamber R27 communicateswith the exterior through the communication holes 468, 470.

In the master cylinder device 402 in which the communication holes areformed thus, to the communication hole 466, an input pressure passage230 whose one end is connected to the third fluid chamber 134 of thepressure adjusting valve device 100 is connected at the other endthereof. Additionally, one end of an external communication passage 382is connected to the communication hole 460, thus the opposing chamberR26 and the inter-piston chamber R28 can communicate with the reservoir62. Therefore, in the master cylinder device 402, a mechanism includingthe open/close valve 384 and the external communication passage 382constitutes a low-pressure-source communication mechanism for theopposing and inter-piston chambers which allows the opposing chamber R26and the inter-piston chamber R28 to communicate with the reservoir 62.Incidentally, in the master cylinder device 402, the reaction forcegenerating device 250 is not provided. Additionally, one end of the lowpressure passage 388 communicating with the low pressure source isconnected to the communication hole 470, thus the internal chamber R27can communicate with the reservoir 62.

<<Actuation of Hydraulic Brake System>>

Actuation of the hydraulic brake system 400 will be described below. Inthe normal condition, that is, in a condition in which the hydraulicbrake system 400 can be actuated normally, the brake fluid whosepressure is adjusted according to the target hydraulic brake force isinputted into the input chamber R25. The first pressurizing piston 406moves forward depending on the pressure of the brake fluid in the inputchamber R25 so as to pressurize the brake fluid in the firstpressurizing chamber R3 and then pressurize the brake fluid in thesecond pressurizing chamber F4.

As described above, in the first pressurizing piston 406, since thepressurized area on which the pressure of the brake fluid in theopposing chamber R26 acts and the pressurized area on which the pressureof a brake fluid in the inter-piston chamber R28 acts are equal, thefirst pressurizing piston 406 is moved depending on not the pressure ofthe brake fluid in the opposing chamber R26 and the pressure of thebrake fluid in the inter-piston chamber R28 but the pressure of thebrake fluid from the high pressure source device 58. Additionally, amovement of the first pressurizing piston 406 does not cause anymovement of the input piston 410. That is, the master cylinder device402 is configured such that the first pressurizing piston 406 and theinput piston 410 can move independently from each other in the normalcondition. Accordingly, in the master cylinder device 402, thehigh-pressure-source-pressure dependent pressurizing state is realizedin the normal condition.

Moreover, in the normal condition, since a total volume of the opposingchamber R26 and the inter-piston chamber R28 is constant, the rodportion 436 and the movable portion 438 in the input piston 410 moverelative to each other with the brake fluid in the internal chamber R27being flowed out when the operation force is applied to the brake pedal70. In other words, the rod portion 436 and the movable portion 438 moverelative to each other so that the input piston 410 shrinks.Additionally, as it shrinks, the elastic reaction force with a magnitudeaccording to an amount of the shrink of the input piston 410 isgenerated by the springs 440, 442. That is, in the master cylinderdevice 402, a mechanism including the springs 440, 442 serves anelastic-reaction-force applying mechanism for the input piston whichapplies the elastic reaction force with the magnitude according to theamount of the shrink of the input piston 410 to the base end portion 434and the movable portion 438, as a reaction force applying mechanismwhich enables the driver to feel the elastic reaction force.Incidentally, since the spring constants of the springs 440, 442 aredifferent from each other, the spring 440 with the small spring constantmainly shrinks until a certain operation amount, and then only thespring 442 with the large spring constant will shrink after the spring440 cannot shrink any more. That is, the master cylinder device 402 isconfigured such that, as the operation amount of the brake pedal 70increases, a ratio of increase of the operation reaction force increasesowing to the two springs 440, 442.

In the large-brake-force-required condition, the open/close valve 384 isde-energized to be opened in the hydraulic brake system 400. Therefore,the input piston 410 moves forward with the brake fluids in theinter-piston chamber R28 and the opposing chamber R26 being flowed intothe reservoir 62. Therefore, when the input piston 410 comes into anabutting contact with the bottom face of the rearward-open blind hole ofthe first pressurizing piston 406, the first pressurizing piston 406 canbe moved forward by the operation force. That is, it is possible topressurize the brake fluids in the pressurizing chambers R3, R4depending on not only the pressure of the brake fluid from the highpressure source device 58 but also the operation force. Accordingly, inthe master cylinder device 402, theoperation-force/high-pressure-source-pressure dependent pressurizingstate is realized in the large-brake-force-required condition.Therefore, the first pressurizing piston 406 can be considered apressure receiving piston which pressurizes the brake fluid to besupplied to the brake devices 56 by receiving the operation force or thepressure of the brake fluid supplied to the input chamber R25. In thelarge-brake-force-required condition, the open/close valve 390 is alsode-energized to be closed, thereby hermetically closing the internalchamber R27, that is, prohibiting the shrink of the input piston 410.That is, in the master cylinder device 402, a mechanism including thelow pressure passage 388 and the open/close valve 390 constitutes aninput-piston-shrink prohibiting mechanism which prohibits the shrink ofthe input piston 410. Therefore, the brake operation force by the driveris transmitted to the first pressurizing piston 406 without shrinkingthe input piston 410, that is, without generating an ineffective brakeoperation amount. Since the pressure of the brake fluids in thepressurizing chambers R3, R4 is transmitted to the input piston 410, thedriver can feel the rearward bias force associated with the pressure asthe operation reaction force.

In a condition in which electric power is not supplied to the hydraulicbrake system 400 due to an electric failure, the open/close valve 384 isde-energized to be opened and the open/close valve 390 is de-energizedto be closed. Therefore, as in theoperation-force/high-pressure-source-pressure dependent pressurizingstate, the first pressurizing piston 406 can move forward depending onthe operation force. That is, in the master cylinder device 402, theoperation-force dependent pressurizing state is realized.

In the master cylinder device 402, the input piston 410 is not fitted tothe first pressurizing piston 406 with any seal. Therefore, even whenthe first pressurizing piston 406 is moved by the pressure of the brakefluid in the input chamber R25, no force resulting from any frictionforce of any seal acts on the input piston 410. In addition, each of thehigh-pressure seals 444, 446 between the first pressurizing piston 406and the housing 404 causes a comparatively large friction force upon amovement of the first pressurizing piston 406, whereas each of the seals448, 450 between the input piston 410 and the housing 404 causes acomparatively small friction force upon a movement of the input piston410. Therefore, in the master cylinder device 402, operational feelingin a brake operation is excellent. Especially in the operation-forcedependent pressurizing state, it is possible to provide excellentoperational feeling.

Fourth Embodiment

FIG. 7 schematically represents a hydraulic brake system 500 of thefourth embodiment. The hydraulic brake system 500 has a master cylinderdevice 502. The hydraulic brake system 500 generally has the samestructure as any one of the hydraulic brake systems of the first throughthird embodiments. In the following description, with consideration forabbreviating the explanation, different construction and actuation fromthe hydraulic brake systems will be described but the same constructionand actuation as the hydraulic brake systems are omitted.

<<Structure of Master Cylinder Device>>

The master cylinder device 502 is categorized into the Input Piston FreeType Master Cylinder, and has a housing 504 being a casing, a firstpressurizing piston 506 and a second pressurizing piston 508 whichpressurize the brake fluid to be supplied to the brake devices 56, andan input piston 510 to which an operation of the driver is inputted viathe operation device 52.

The housing 504 mainly includes four members, specifically, a firsthousing member 512, a second housing member 514, a third housing member516, and a fourth housing member 518, and has a roughly hollowcylindrical shape whose front end is closed. Among the housing members,the second housing member 514 has a hollow cylindrical shape in which aninner flange 520 is formed at a rear end portion. In addition, the innerflange 520 defines a through hole 522 at a rear end of the secondhousing member 514. An interior of the housing 504 constructed thus isseparated by the inner flange 520 of the second housing member 514 todefine a front side chamber R31 located in a front side and a rear sidechamber R32 located in a rear side. That is, the inner flange 520 servesas a partition portion separating the interior of the housing 504, andthe through hole 522 serves as an opening of the partition portion.

The second pressurizing piston 508 has a hollow cylindrical shape whoserear end portion is closed, and is slidably fitted with seals in thefirst housing member 512 in the front side chamber R31. The firstpressurizing piston 506 includes a main body portion 526 located in thefront side chamber R31 and having a hollow cylindrical shape whose rearend portion is closed, and an extension portion 522 extending from arear end portion of the main body portion 526 through the through hole522 into the rear side chamber R32. Additionally, on an outer peripheryof a bottom portion of the main body portion 526, there is provided aflange 530. The first pressurizing piston 506 is fitted with seals inthe housing 504 such that a front portion of the main body portion 526slidably contacts with the first housing member 512, the flange 530slidably contacts with the second housing member 512, and the extensionportion 528 slidably contacts with the through hole 522 of the secondhousing member 512. The input piston 510 is disposed in the rear sidechamber R32 and is fitted, behind the extension portion 528 of the firstpressurizing piston 506, in the third housing member 516. The inputpiston 510 has a roughly a hollow cylindrical shape and is connected, ata separation wall 532 provided in an interior thereof, to the operationrod 72. In addition, a flange is provided on an outer periphery of afront end portion of the input piston 510, whose a rearward movement islimited by that the flange is stopped by the third housing member 516.

In the master cylinder device 502 constructed thus, between the mainbody portion 526 of the first pressurizing portion 506 and the innerflange 520 of the second housing member 512, there is defined a fluidchamber R35 into which the brake fluid from the high pressure sourcedevice 58 is inputted. This fluid chamber R35 is referred to as an“input chamber”, where appropriate. Additionally, between an innercircumferential face of the second housing member 514 in front of theflange 530 and an outer circumferential face of the first pressurizingpiston 506, there is defined an annular fluid chamber R36 opposing theinput chamber R35 with the flange 530 being interposed between theopposing chamber R36 and the input chamber R35. Hereinafter, thischamber is referred to as an “opposing chamber”, where appropriate. Inaddition, between a rear end face of the extension portion 528 of thefirst pressurizing piston 506 and a front end face of the input piston510, there is provided a clearance which is small in no brake operation.In a space around the extension portion 528 including the aboveclearance, there is defined an inter-piston chamber R38. Additionally,in the first pressurizing piston 506, a pressurized area on which apressure of a brake fluid in the inter-piston chamber R38 acts, namely,an area of the rear end face of the extension portion 528, and apressurized area on which a pressure of a brake fluid in the opposingchamber R36 acts, namely, an area of the front end face of the flange530 are equal.

In the master cylinder device 502 in which each of the chambers isdefined thus, the input chamber R35 is defined by that the firstpressurizing piston 506 contacts with the inner circumferential face ofthe second housing member 514 via a seal 540 embedded in an outercircumferential face of the flange 530 and contacts with an innercircumferential face defining the through hole 522 of the second housingmember 514 via a seal 542 embedded in an inner circumferential facedefining the through hole 522. By the way, the input piston 510 slidablycontacts with an inner circumferential face of the third housing member516, and seals 544, 546 are embedded in an inner circumferential face ofa rear end portion of the third housing member 516. It is noted that ahigh-pressure seal is employed as each of the seals 540, 542 but notemployed as each of the seals 544, 546.

In the first housing member 512, there is provided a communication hole560 whose one end is open to the opposing chamber R36. In the secondhousing member 514, there is provided a communication hole 562 whose oneend is open so as to face the other end of the communication hole 560,and furthermore, in the fourth housing member 518, there is provided acommunication hole 564 whose one end is open so as to face the other endof the communication hole 562 and whose other end is open to theexterior. That is, the opposing chamber R36 communicates with theexterior through the communication holes 560, 562, 564. In addition, inthe second housing member 514, there is provided a communication hole566 whose one end is open to the input chamber R35, and, in the fourthhousing member 518, there is provided a communication hole 568 whose oneend is open so as to face the other end of the communication hole 566and whose other end is open to the exterior. That is, the input chamberR35 communicates with the exterior through the communication holes 566,568.

Since an inner diameter of a part of the rear end portion of the thirdhousing member 516 is slightly larger than an outer diameter of acircumferential wall of the input piston 510, a fluid passage 570 isformed between a rear end portion and the circumferential wall of theinput piston 510. In addition, between an outer circumferential face ofthe third housing member 516 and an inner circumferential face of thefourth housing member 518, there is formed a fluid passage 572 since anouter diameter of the third housing member 516 and an inner diameter ofthe fourth housing member 518 are different from each other. In thecircumferential wall of the input piston 510, there is provided acommunication hole 574 whose one end is open to the inter-piston chamberR38 and whose other end is open to the fluid passage 570. In the thirdhousing member 516, there is provided a communication hole 576 whose oneend is open to the fluid passage 570 between the seal 544 and the seal546 and whose other end is open to the fluid passage 572. Moreover, inthe fourth housing member 518, there is provided a communication hole578 whose one end is open to the fluid passage 572 and whose other endis open to the exterior. That is, the inter-piston chamber R38communicates with the exterior through the communication hole 574, thefluid passage 570, the communication hole 576, the fluid passage 572,and the communication hole 578.

In addition, in a front end portion of the third housing member 516,there is provided a communication hole 580 whose one end is open to theinter-piston chamber R38, and, in the fourth housing member 518, thereis provided a communication hole 582 whose one end is open so as to facethe other end of the communication hole 580 and whose other end is opento the exterior.

In the master cylinder device 502 in which the communication holes areformed thus, to the communication hole 568, an input pressure passage230 whose one end is connected to the third fluid chamber 134 of thepressure adjusting valve device 100 is connected at the other endthereof. Moreover, one end of an external communication passage 584 isconnected to the communication hole 564, and the other end thereof isconnected to the communication hole 582. Therefore, in the mastercylinder device 502, the external communication passage 584 constitutesan inter-chamber communication passage which allows a communicationbetween the opposing chamber R36 and the inter-piston chamber R38. Inaddition, an electromagnetic open/close valve 586 which is anormally-closed valve is provided on the external communication passage584. Further, a low pressure passage 588 communicating with thereservoir 62 through the communication hole 578 diverges from between anend portion connected to the communication hole 564 and the open/closevalve 586 in the external communication passage 584, and anelectromagnetic open/close valve 590 which is a normally-opened valve isprovided on the low pressure passage 588. Therefore, the opposingchamber R36 and the inter-piston chamber R38 can communicate with thereservoir 62, thus a mechanism including the external communicationpassage 584, the open/close valve 586, the low pressure passage 588, andthe open/close valve 590 constitutes a low-pressure-source communicationmechanism for the opposing and inter-piston chambers which allows theopposing chamber R36 and the inter-piston chamber R38 to communicatewith the reservoir 62. Moreover, in the low pressure passage 588, thereis provided a check valve 591 in parallel with the open/close valve 590in order that each of the pressures of the brake fluids in the opposingchamber R36 and the inter-piston chamber R38 does not become lower thana pressure of the brake fluid in the reservoir 62. In the low pressurepassage 588, a reaction force generating device 250 into/from which thebrake fluid flows from/into the master cylinder device 502 is providedbetween a diverging point from the external communication passage 584and the open/close valve 590. Therefore, in a state in which theopen/close valve 590 is closed, when a total volume of the opposingchamber R36 and the inter-piston chamber R38 decreases, the volume ofthe fluid storage chamber R9 of the reaction force generating device 250increases.

a communication passage 592 diverging from between the end connected tothe communication hole 582 and the open/close valve 584 in the externalcommunication passage 584 is connected to the pressure adjusting valvedevice 100 of the pressure-intensifying/reducing device 60,specifically, the first fluid chamber 130 of the pressure adjustingvalve device 100. That is, in the hydraulic brake system 500, thepressure adjusting valve device 100 can be activated by utilizing, asthe pilot pressure, not the master pressure but the pressure of thebrake fluid in the inter-piston chamber R38. In addition, anelectromagnetic open/close valve 594 which is a normally-opened valve isprovided on the external communication passage 592.

<<Actuation of Hydraulic Brake System>>

Actuation of the hydraulic brake system 500 will be described below. Ina normal condition, that is, in a condition in which the hydraulic brakesystem 500 can be actuated normally, the open/close valve 590 isenergized to be closed and the open/close valve 594 is energized to beclosed. In this state, the brake fluid whose pressure is adjustedaccording to the target hydraulic brake force is inputted into the inputchamber R35. The first pressurizing piston 506 moves forward dependingon the pressure of the brake fluid in the input chamber R35 so as topressurize the brake fluid in the first pressurizing chamber R3 and thenpressurize the brake fluid in the second pressurizing chamber R4.

As described above, in the first pressurizing piston 506, since thepressurized area on which the pressure of the brake fluid in theopposing chamber R36 acts and the pressurized area on which the pressureof a brake fluid in the inter-piston chamber R38 acts are equal, thefirst pressurizing piston 506 as the pressure receiving piston is moveddepending on not the pressure of the brake fluid in the opposing chamberR36 and the pressure of the brake fluid in the inter-piston chamber R38but the pressure of the brake fluid from the high pressure source device58. Additionally, a movement of the first pressurizing piston 506 doesnot cause any movement of the input piston 510. That is, the mastercylinder device 502 is configured such that the first pressurizingpiston 506 and the input piston 510 can move independently from eachother in the normal condition. Accordingly, in the master cylinderdevice 502, a “high-pressure-source-pressure dependent pressurizingstate”, that is, a state in which the brake fluid supplied to the brakedevices 56 can be pressurized depending on the pressure of the brakefluid introduced from the high pressure source device 58 is realized inthe normal condition.

Additionally, in the normal condition, when the input piston 510 movesforward relative to the first pressurizing piston 506 in accordance withan increase of the operation amount, and then the brake fluid in theinter-piston chamber R38 flows out, therefore the total volume of theopposing chamber R36 and the inter-piston chamber R38 decreases. Theoutflowed brake fluid flows into the fluid storage chamber R9 of thereaction force generating device 250, each of the pressures of the brakefluids in the opposing chamber R36, the inter-piston chamber R38, andthe fluid storage chamber R9 increases. The pressure of the brake fluidin the inter-piston chamber R38 acts on the input piston 510, thereforea rearward bias force is applied to the input piston 510, whereby thedriver can feel the bias force as an operation reaction force against abrake operation by the driver.

In the large-brake-force-required condition, the open/close valve 586 isde-energized to be closed and the open/close valve 590 is de-energizedto be opened in the hydraulic brake system 500. Therefore, the firstpressurizing piston 506 moves forward with the brake fluids in theopposing chamber R36 being flowed into the reservoir 62. Therefore, inthe master cylinder device 502, a mechanism including the open/closevalve 590 constitutes a low-pressure-source communication mechanism forthe opposing chamber which allows the opposing chamber R36 tocommunicate with the reservoir 62. In addition, when the input piston ismoved forward in this state, the communication hole 574 provided in theinput piston 510 passes over the seal 544, whereby the communicationbetween the communication hole 576 of the third housing member 516 andthe communication hole 574 is shut off. That is, in thelarge-brake-force-required condition, since the open/close valve 586 isclosed and the communication between the communication hole 574 and thecommunication hole 576 is shut off, the communication between theinter-piston chamber R38 and the reservoir 62 is shut off. Therefore, inthe master cylinder device 502, a mechanism including the open/closevalve 586, the seal 544, and the communication holes 574, 576 isconsidered an inter-piston-chamber hermetically closing mechanism.Therefore, the brake operation force by the driver is transmitted fromthe input piston 510 via the brake fluid in the inter-piston chamber R38to the first pressurizing piston 506. Accordingly, in the mastercylinder device 502, the operation-force/high-pressure-source-pressuredependent pressurizing state is realized in thelarge-brake-force-required condition. Therefore, the first pressurizingpiston 506 can be considered a pressure receiving piston whichpressurizes the brake fluid to be supplied to the brake devices 56 byreceiving the operation force or the pressure of the brake fluidsupplied to the input chamber R35. Incidentally, in theoperation-force/high-pressure-source-pressure dependent pressurizingstate, since the pressure of the brake fluids in the pressurizingchambers R3, R4 is transmitted to the input piston 510, the driver canfeel the rearward bias force generated by the pressure as the operationreaction force.

In a condition in which electric power is not supplied to the hydraulicbrake system 500 due to an electric failure, the open/close valves 586,590 are put in the same respective states as in theoperation-force/high-pressure-source-pressure dependent pressurizingstate. That is, it is possible to pressurize the brake fluids in thepressurizing chambers R3, R4 depending on the operation force so as tosupply the brake fluid to the brake devices 56FL, 56FR. That is, in themaster cylinder device 502, the operation-force dependent pressurizingstate is realized. Moreover, in the hydraulic brake system 500, theopen/close valve 594 is de-energized to be opened in the electricfailure condition etc. Therefore, the pressure adjusting valve device100 can be activated by utilizing, as the pilot pressure, the pressureof the brake fluid in the inter-piston chamber R38. Therefore, unlikeutilizing, as the pilot pressure, the master pressure which is affectedby a friction force etc. upon a movement of the first pressurizingpiston 506, the activation of the pressure adjusting valve device 100 iscomparatively favorable in an ability of following a change of brakeoperation.

In the master cylinder device 502, the input piston 510 is not fitted tothe first pressurizing piston 506 with any seal. Therefore, even whenthe first pressurizing piston 506 is moved by the pressure of the brakefluid in the input chamber R35, no force resulting from any frictionforce of any seal acts on the input piston 510. In addition, each of thehigh-pressure seals 540, 542 between the first pressurizing piston 506and the housing 504 causes a comparatively large friction force upon amovement of the first pressurizing piston 506, whereas each of the seals544, 546 between the input piston 510 and the housing 504 causes acomparatively small friction force upon a movement of the input piston510. Therefore, in the master cylinder device 502, operational feelingin a brake operation is excellent. Especially in the operation-forcedependent pressurizing state, it is possible to provide excellentoperational feeling.

Fifth Embodiment

FIG. 8 schematically represents a hydraulic brake system 600 of thefifth embodiment. The hydraulic brake system 600 has a master cylinderdevice 602 and an antilock device 603. The hydraulic brake system 600generally has the same structure as any one of the hydraulic brakesystems of the first through fourth embodiments. In the followingdescription, with consideration for abbreviating the explanation,different construction and actuation from the hydraulic brake systemswill be described but the same construction and actuation as thehydraulic brake systems are omitted.

<<Structure of Master Cylinder Device>>

The master cylinder device 602 is categorized into the Master-Cut SystemAdoptable Type Master Cylinder Device, and has a housing 604 being acasing, a first pressurizing piston 606 and a second pressurizing piston608 which pressurize the brake fluid to be supplied to the brake devices56, an intermediate piston 610 which can move forward by the brake fluidintroduced from the high pressure source device 58, and an input piston612 to which an operation of the driver is inputted via the operationdevice 52.

The housing 604 mainly includes two members, specifically, a firsthousing member 614 and a second housing member 616. The first housingmember 614 has a roughly hollow cylindrical shape whose front end isclosed. The first housing member 614 is sectioned into two portionshaving mutually different inner diameters, specifically, asmall-inner-diameter portion 618 arranged in a front side and having asmall inner diameter, and a large-inner-diameter portion 620 arranged ina rear side and having a large inner diameter. The second housing member616 has a roughly hollow cylindrical shape, and is sectioned into twoportions having mutually different outer diameters, specifically, asmall-outer-diameter portion 624 arranged in a front side and having asmall outer diameter, and a large-outer-diameter portion 626 arranged ina rear side and having a large outer diameter.

In the housing 604 constructed above, the large-outer-diameter portion626 of the second housing member 616 serves an annular separation wallportion projecting to the inside in a radial direction, and thesmall-outer-diameter portion 624 serves an inner cylindrical portionextending forward from an inner periphery of the separation wallportion. In other words, in the housing 604, a partition portionseparating an interior of the housing 604 is formed by thesmall-outer-diameter portion 624 and the large-outer-diameter portion626 of the second housing member 616. Therefore, the interior of thehousing 604 is separated into a front side chamber R41 including anoutside space of the small-outer-diameter portion 624 and a rear sidechamber R42 including an inside space of the small-outer-diameterportion 624. In addition, a front end of the small-outer-diameterportion 624 serves as an opening formed in the partition portion.

Each of the first pressurizing piston 606 and the second pressurizingpiston 608 has a hollow cylindrical shape whose rear end portion isclosed, and is slidably fitted with seals in the small-inner-diameterportion 618 of the first housing member 614 in the front side chamberR41. The intermediate piston 610 includes a main body portion disposedin the front side chamber R41 and having a hollow cylindrical shape, anda rear side portion of the main body portion serves as a cylindricalportion 628 which has a blind hole being open rearward and a hollowcylindrical shape. The intermediate piston 610 is fitted with seals inthe housing 604 such that an outer circumferential face slidablycontacts with the large-inner-diameter portion 620 of the first housingmember 614, and an inner circumferential face of the cylindrical portion628 slidably contacts with the small-outer-diameter portion 624 of thesecond housing member 616. That is, the intermediate piston 610 isdisposed such that the small-outer-diameter portion 624 of the secondhousing member 616 is inserted in the cylindrical portion 628, in otherwords, such that the cylindrical portion 628 is interposed between thelarge-inner-diameter portion 620 of the first housing member 614 and thesmall-outer-diameter portion 624 of the second housing member 616. So tospeak, the large-inner-diameter portion 620 of the first housing member614 can be considered to be an outer cylindrical portion of the housing604. In addition, between a rear end face of the first pressurizingpiston 606 and a front end face of the intermediate piston 610, there isa clearance which is small in no brake operation. The input piston 612has a shape roughly like a cylinder and is located in the rear sidechamber R42. Specifically, the input piston 612 is fitted in thesmall-outer-diameter portion 624 of the second housing member 616 withseals. Accordingly, in the master cylinder device 602, since a part ofthe intermediate piston 610 and the input piston 612 overlap with eachother in the front-back direction, the entire length of the mastercylinder device 602 is comparatively short.

In the master cylinder device 602 constructed thus, between a rear endof the main body portion of the intermediate piston 610 and the secondhousing member 616, there is defined a fluid chamber R45 into which thebrake fluid from the high pressure source device 58 is inputted. Thisfluid chamber R45 is referred to as an “input chamber”, whereappropriate. It is noted that the input chamber R45 is illustrated in analmost squeezed state in FIG. 8. In addition, a bottom face of the blindhole of the intermediate piston 610 and a front end face of the inputpiston 612 separate away from each other in no brake operation.Including a space formed by the separation, an inter-piston chamber R48is defined between the intermediate piston 610 and the input piston 612.

In the master cylinder device 602 in which each of the chambers isdefined thus, the input chamber R45 is defined by that the intermediatepiston 610 contacts with an inner circumferential face of the firsthousing member 614 via a seal 640 embedded in the outer circumferentialface of the intermediate piston 610 and contacts with an outercircumferential face of the small-outer-diameter portion 624 of thesecond housing member 616 via a seal 642 embedded in an innercircumferential face of the intermediate piston 610. By the way, theinput piston 612 slidably contacts with an inner circumferential face ofthe small-outer-diameter portion 624 of the second housing member 616,and seals 644, 646 are embedded in an outer circumferential face of theinput piston 612. It is noted that a high-pressure seal is employed aseach of the seals 640, 642 but not employed as each of the seals 644,646.

In the master cylinder device 602, there is provided an atmosphericpressure chamber 660 between an outer circumferential face of a rear endportion of the first pressurizing piston 606 and an innercircumferential face of an intermediate portion of the firstpressurizing piston 614. The atmospheric pressure chamber 660 isprovided in the first housing member 614, and is maintained at theatmospheric pressure at all times by a fluid passage 662 whose one endis open to the atmospheric pressure chamber 660 and whose other end isopen to the above described communication hole 214 communicating withthe reservoir 62. Additionally, in the first housing member 614, thereis provided a communication hole 664 whose one end is open to theatmospheric pressure chamber 660 and whose other end is open to theexterior.

Since the outer diameter of a part of the cylindrical portion 628 issmall, there is provided a fluid passage between thelarge-inner-diameter portion 620 of the first housing member 614 and thecylindrical portion 628 of the intermediate piston 610. Additionally,between the inner circumferential face of the cylindrical portion 628 ofthe intermediate piston 610 and the outer circumferential face of thesmall-outer-diameter portion 624 of the second housing member 616, thereis provided a clearance having a certain cross section area throughwhich the brake fluid can flow, though it is hard to be seen from thefigure. In the first housing member 614, there is provided acommunication hole 666 whose one end is open to the fluid passage andwhose other end is open to the exterior. Additionally, in theintermediate piston 610, there is provided a communication hole 668whose one end is open to the clearance and whose other end is open tothe fluid passage. Therefore, the inter-piston chamber R48 communicateswith the exterior through the clearance, the communication hole 668, thefluid passage, and the communication hole 666. Moreover, in the firsthousing member 614, there is provided a communication hole 672 whose oneend is open to the input chamber R45 and whose other end is open to theexterior. Therefore, the input chamber R45 communicates with theexterior.

In the master cylinder device 602 in which the communication holes areformed thus, to the communication hole 672, an input pressure passage230 whose one end is connected to the third fluid chamber 134 of thepressure adjusting valve device 100 is connected at the other endthereof. Moreover, one end of an external communication passage 674 isconnected to the communication hole 664 which communicates with theatmospheric pressure chamber 660 being at the atmospheric pressure, andthe other end thereof is connected to the communication hole 666.Therefore, the inter-piston chamber R48 can communicate with thereservoir 62. In addition, an electromagnetic open/close valve 676 whichis a normally-opened valve is provided on the external communicationpassage 674. In the external communication passage 674, a reaction forcegenerating device 250 into/from which the brake fluid flows from/intothe master cylinder device 602 is provided between the end connected tothe communication hole 666 and the open/close valve 676. Therefore, in astate in which the open/close valve 676 is closed, when the volume ofthe inter-piston chamber R48 decreases, the volume of the fluid storagechamber R9 of the reaction force generating device 250 increasesaccording to the decrease.

Electromagnetic open/close valves 680, 682 (hereinafter, each of whichis referred to as a “master-cut valve”, where appropriate) each of whichopens in a de-energized state and closes in an energized state areprovided on fluid passages 80, 82, respectively. In the hydraulic brakesystem 600, the open/close of those master-cut valves 680, 682selectively realize a state in which a supply of the brake fluidpressurized by the master cylinder device 602 to the brake devices 56FL,FR is allowed and a state in which the supply is prohibited.

<<Structure of Antilock Device>>

Unlike the above hydraulic brake system employing the Input Piston FreeType Master Cylinder Device, a pressure intensifying communicationpassage 684 for supplying the pressure-adjusted brake fluid to the brakedevices 56 diverges from the input pressure passage 230 connecting thepressure adjusting valve device 100 to the master cylinder device 50.The pressure intensifying communication passage 684 is connected to theantilock device 603. Inside the antilock device 603, the pressureintensifying communication passage 684 diverges into four passages.These diverging four pressure intensifying communication passages areeach connected to the brake devices 56 via electromagneticpressure-intensifying open/close valves 686. In addition, a pressurereducing communication passage 688 is connected to the reservoir 62.Inside the antilock device 603, the pressure reducing communicationpassage 688 also diverges into four passages. These diverging fourpressure reducing communication passages are each connected to the brakedevices 56 via an electromagnetic pressure-reducing open/close valve690. Incidentally, among four pressure-intensifying open/close valves686, the pressure-intensifying open/close valves 686FL, FR correspondingto the brake devices 56FL, FR are normally-closed valve, and the othertwo pressure-intensifying open/close valves 686 and the fourpressure-reducing open/close valves 690 are normally-opened valves.

<<Actuation of Hydraulic Brake System>>

In the hydraulic brake system 600, when the input piston 612 movesforward relative to the intermediate piston 610, the brake fluid in theinter-piston chamber R48 flows out. When the open/close valve 676 isclosed, the outflowed brake fluid flows into the fluid storage chamberR9 of the reaction force generating device 250. Therefore, the brakefluids in the inter-piston chamber R48 and the fluid storage chamber R9increase. Then, the intermediate piston 610 can be moved forward by theoperation force. In addition, when the brake fluid in the inter-pistonchamber R48 flows out and then the input piston 612 comes into abuttingcontact with the intermediate piston 610, the intermediate piston 610 isalso moved by the operation force. Moreover, the intermediate piston 610can be also moved by the pressure in the brake fluid in the inputchamber R45, that is, the pressure of the brake fluid from the highpressure source device 58. That is, the intermediate piston 610 can beconsidered a pressure receiving piston which pressurizes the brake fluidto be supplied to the brake devices 56 by receiving the operation forceor the pressure of the brake fluid supplied to the input chamber R45.Accordingly, the master cylinder device 602 of the hydraulic brakesystem 600 is configured to realize theoperation-force/high-pressure-source-pressure dependent pressurizingstate at all times. Incidentally, the above pressure of the brake fluidin the inter-piston chamber R48 acts on the input piston 612, thereforea rearward bias force is applied to the input piston 612, whereby thedriver can feel the bias force as an operation reaction force against abrake operation by the driver.

In this hydraulic brake system 600, the master-cut valves 680, 682 areenergized to be closed in the normal condition. Therefore, thepressurizing chambers R3, R4 are hermetically closed, thus thepressurizing pistons 606, 608 can hardly move forward, and the brakefluid is not supplied from the master cylinder device 602 to the brakedevice 56 in the normal condition. Meanwhile, the pressure-intensifyingopen/close valve 686 is opened, thus the pressure-intensified brakefluid is supplied to the brake device 56 through the pressureintensifying communication passage 684. Consequently, the brake device56 can generate the hydraulic brake force depending on only the pressureof the brake fluid. That is, in the brake device 56, a state in whichthe hydraulic brake force with a magnitude dependent on thehigh-pressure-source pressure is realized in the normal condition. So tosay, in the master cylinder device 602, shutting (cutting) off thecommunication between the master cylinder device 602 and the brakedevice 56 realizes the state in which the hydraulic brake force with amagnitude dependent on only the high-pressure-source pressure isgenerated. Incidentally, the open/close valve 676 is energized to beclosed in the normal condition.

In the large-brake-force-required condition, the master-cut valves 680,682 are de-energized to be opened and the pressure-intensifyingopen/close valves 686FL, FR are de-energized to be closed in thehydraulic brake system 600. Therefore, the brake fluid is supplied tothe brake devices 56FL, FR from the master cylinder device 602 in theoperation-force/high-pressure-source-pressure dependent pressurizingstate, and the supply of the brake fluid from the pressure adjustingvalve device 100 is shut off. Consequently, in the brake devices 56FL,FR, a state in which the hydraulic brake force with a magnitudedependent on the high-pressure-source pressure plus a hydraulic brakeforce with a magnitude dependent on the operation force is generated isrealized in the large-brake-force-required condition. Incidentally,since the open/close valve 676 is de-energized to be opened in thelarge-brake-force-required condition, the input piston 612 moves forwardwith the brake fluid in the inter-piston chamber R48 being flowed intothe reservoir 62 so as to comes into an abutting contact with the bottomface of the blind hole of the intermediate piston 610. It is noted that,since the brake fluids in the pressurizing chambers R3, R4 are suppliedonly to the brake devices 56FL, FR in the large-brake-force-requiredcondition, the brake fluid is supplied only to the brake devices 56 inthe front wheels from the master cylinder device 602. Additionally,since the pressure of the brake fluids in the pressurizing chambers R3,R4 is transmitted to the input piston 612, the driver can feel arearward bias force generated by the pressure as the operation reactionforce.

As a result, in the hydraulic brake system 600, the open/close of eachof the master-cut valves 680, 682 and the pressure-intensifyingopen/close valves 686FL, FR is controlled in order to supply the brakefluid from one of the master cylinder device 602 and the pressureadjusting valve device 100 each of which is a supply source of the brakefluid to the brake devices 56FL, FR. That is, a mechanism including themaster-cut valves 680, 682 and the pressure-intensifying open/closevalves 686FL, FR can be considered to be a switching mechanism forswitching the supply source of the brake fluid to the brake devices56FL, 56FR.

In the hydraulic brake system 600, a switch from a state in which thebrake devices 56FL, 56FR generate the hydraulic brake force with amagnitude dependent on the high-pressure-source pressure to a state inwhich they generate the hydraulic brake force with a magnitude dependenton the high-pressure-source pressure and the operation force is carriedout when the pressure of the brake fluid supplied from the pressureadjusting device 100 to the brake devices 56FL, FR is approximatelyequal to the pressure of the brake fluid supplied from the mastercylinder device 602 to the brake devices 56FL, FR. Therefore, thepressure of the brake fluid to be supplied to the brake devices 56FL, FRhardly change before and after the switch, and therefore the switch canbe carried out without changing the hydraulic brake force generating inthe brake devices 56FL, FR. Accordingly, the switch can be carried outwithout giving a driver unfavorable feeling. Therefore, in the mastercylinder device 602, a pressurized area of the first pressurizing piston606 on which a pressure of the first pressurizing chamber R3 acts and apressurized area of the second pressurizing piston 608 on which apressure of the second pressurizing chamber R4 acts are set such thatthe pressure of the brake fluids in the pressurizing chambers R3, R4 andthe pressure of the brake fluid supplied from the pressure adjustingdevice 100 to the brake devices 56 be almost equal. Specifically, eachof those pressurized areas is smaller by a degree corresponding to theconsidered operation force than a pressurized area of the intermediatepiston 610 on which the pressure of the brake fluid in the input chamberR45 acts.

In a condition in which electric power is not supplied to the hydraulicbrake system 600 due to an electric failure, each of the open/closevalve 676, the master-cut valves 680, 682, and the pressure-intensifyingopen/close valves 686FL, FR is de-energized to come into the sameopen/close state as in the large-brake-force-required condition.Accordingly, in the master cylinder device 602, an “operation-forcedependent pressurizing state”, that is, a state in which the brakefluids in the pressurizing chambers R3, R4 are pressurized depending ononly the operation force is realized. That is, in the brake devices56FL, FR, a state in which the hydraulic brake force with a magnitudedependent on only the operation force is realized. Incidentally, whenthe pressure-intensified brake fluid is stored in the accumulator 92 ofthe high pressure source device 58, the pressure of thepressure-intensified brake fluid assists the pressurizing of the brakefluids in the pressurizing chambers R3, R4.

In the master cylinder device 602, the input piston 612 is not fitted tothe intermediate piston 610 with any seal. Therefore, even when theintermediate piston 610 is moved by the pressure of the brake fluid inthe input chamber R45, no force resulting from any friction force of anyseal acts on the input piston 612. In addition, each of thehigh-pressure seals 640, 642 between the intermediate piston 610 and thehousing 604 causes a comparatively large friction force upon a movementof the intermediate piston 610, whereas each of the seals 644, 646between the input piston 612 and the housing 604 causes a comparativelysmall friction force upon a movement of the input piston 612. Therefore,in the master cylinder device 602, operational feeling in a brakeoperation is excellent especially in the operation-force dependentpressurizing state. So it is possible to provide excellent operationalfeeling especially in the operation-force dependent pressurizing state.

Sixth Embodiment

FIG. 9 schematically represents a hydraulic brake system 700 of thesixth embodiment. The hydraulic brake system 700 has a master cylinderdevice 702 and an antilock device 603. The hydraulic brake system 700generally has the same structure as any one of the hydraulic brakesystems of the first through fifth embodiments. In the followingdescription, with consideration for abbreviating the explanation,different construction and actuation from the hydraulic brake systemswill be described but the same construction and actuation as thehydraulic brake systems are omitted.

<<Structure of Master Cylinder Device>>

The master cylinder device 702 is categorized into the Master-Cut SystemAdoptable Type Master Cylinder Device, and has a housing 704 being acasing, a first pressurizing piston 706 and a second pressurizing piston708 which pressurize the brake fluid to be supplied to the brake devices56, and an input piston 710 to which an operation of the driver isinputted via the operation device 52.

The housing 704 mainly includes two members, specifically, a firsthousing member 712 and a second housing member 714. The first housingmember 712 has a roughly hollow cylindrical shape whose front end isclosed, and is sectioned into three portions having mutually differentinner diameters, specifically, a front small-diameter portion 716arranged in a front side and having a small inner diameter, a rearlarge-diameter portion 718 arranged in a rear side and having a largeinner diameter, and an intermediate portion 720 arranged between theabove two portions and having an inner diameter of a medium size betweenthe above two inner diameters. The second housing member 714 has aroughly hollow cylindrical shape, and is sectioned into a front sideportion 722 arranged in a front side, a rear side portion 724 arrangedin a rear side, and an intermediate portion 726 arranged between theabove two portions and having an outer diameter larger than that of thefront side portion 722 and that of the rear side portion 724.

In the housing 704 constructed above, the intermediate portion 726 ofthe second housing member 714 serves an annular separation wall portionprojecting to the inside in a radial direction, and the front sideportion 722 serves an inner cylindrical portion extending forward froman inner periphery of the separation wall portion. In other words, inthe housing 704, a partition portion separating an interior of thehousing 704 is formed by the intermediate portion 726 and the front sideportion 722. Therefore, the interior of the housing 704 is separatedinto a front side chamber R51 including an outside space of the frontside portion 722 and a rear side chamber R52 including an inside spaceof the front side portion 722. In addition, a front end of the frontside portion 722 serves as an opening formed in the partition portion.

The second pressurizing piston 708 has a hollow cylindrical shape whoserear end portion is closed, and is slidably fitted with seals in thefirst housing member 712 in the front side chamber R51. The firstpressurizing piston 706 includes a main body portion 730 disposed in thefront side chamber R51 and having a roughly hollow cylindrical shape,and a separation wall 732 disposed approximately in the middle of themain body portion 730 in the front-back direction and separating aninterior of the first pressurizing piston 706 in the front-backdirection. Therefore, in the first pressurizing piston 706, a rearportion of the separation wall 732 serves as a cylindrical portion 734including a blind hole being open rearward. The first pressurizingpiston 706 formed thus is fitted with seals in the housing 704 such thata front portion of the main body portion 730 slidably contacts with thefront small-diameter portion 716 of the first housing member 712, andthe cylindrical portion 734 slidably contacts with the intermediateportion 720 of the first housing member 712 and the front side portion722 of the second housing member 714. That is, the first pressurizingpiston 706 is disposed such that the front side portion 722 of thesecond housing member 714 is inserted in the cylindrical portion 734, inother words, such that the cylindrical portion 734 is interposed betweenthe intermediate portion 720 of the first housing member 712 and thefront side portion 722 of the second housing member 714. So to speak,the intermediate portion 720 of the first housing member 712 can beconsidered to be an outer cylindrical portion of the housing 704. Theinput piston 710 roughly has a hollow cylindrical shape whose rear endportion is closed, that is, a shape having a blind hole being openforward. An operation rod 72 is connected to a rear end of the inputpiston 710.

The input piston 710 is inserted in the second housing member 714 andfitted in an inside of the second housing member 714 with seals.Accordingly, in the master cylinder device 702, since a part of thefirst pressurizing piston 706 and a part of the input piston 710 overlapwith each other in the front-back direction when the input piston 710moves forward, the entire length of the master cylinder device 702 iscomparatively short. Additionally, between a bottom face of therearward-opening blind hole of the cylindrical portion 734 of the firstpressurizing piston 706 and a bottom face of the forward-opening blindhole of the input piston 710, two compression coil springs 736, 738 eachof which generates an elastic reaction force in a direction ofseparating the first pressurizing piston 706 and the input piston 710are disposed in series in the front-back direction. It is noted that thespring constant of the spring 738 is smaller than the spring constant ofthe spring 736. Additionally, between the springs 736, 738, a floatingseat 740 is disposed while supported by them.

In the master cylinder device 702 constructed thus, between a rear endof the main body portion 730 of the first pressurizing portion 706 andthe intermediate portion 726 of the second housing member 714, there isdefined a fluid chamber R55 into which the brake fluid from the highpressure source device 58 is inputted. This fluid chamber R55 isreferred to as an “input chamber”, where appropriate. Furthermore,between a bottom face of a rearward-open blind hole of the cylindricalportion 734 of the first pressurizing piston 706 and the input piston710, there is defined an inter-piston chamber R28 across which the inputpiston 710 and the first pressurizing piston 706 face to each other.

In the master cylinder device 702, the first pressurizing piston 706contacts with an inner circumferential face of the intermediate portion720 of the first housing member 712 via seals 742, 744 embedded in anouter circumferential face in a front portion of the cylindrical portion734. Additionally, the input chamber R55 is defined by that the firstpressurizing piston 706 contacts with the inner circumferential face ofthe intermediate portion 720 of the first housing member 712 via a seal746 embedded in an outer circumferential face of the cylindrical portion734 and contacts with an outer circumferential face of the front sideportion 722 of the second housing member 714 via a seal 748 embedded inan inner circumferential face of the cylindrical portion 734. The inputpiston 710 slidably contacts with an inner circumferential face of thesecond housing member 714, and seals 750, 752 are embedded in an innercircumferential face of the second housing member 714. It is noted thata high-pressure seal is employed as each of the seals 746, 748 but notemployed as each of the seals 750, 752.

In the first pressurizing piston 706, there is provided a communicationhole 760 whose one end is open to the inter-piston chamber R58.Additionally, in the first housing member 712, there is provided acommunication hole 762 whose one end is open so as to face the other endof the communication hole 760 and whose other end is open to theexterior. Accordingly, the inter-piston chamber R58 can communicate withthe exterior. It is noted that the other end of the communication hole760 is open between the seal 742 and the seal 744. In a circumferentialwall of the input piston 710, there is provided a communication hole 764whose one end is open to the inter-piston chamber R58. In theintermediate portion 726 of the second housing member 714, there isprovided, between the seal 750 and the seal 752, a communication hole766 whose one end is open so as to face the other end of thecommunication hole 764. Moreover, in the first housing member 712, thereis provided a communication hole 768 whose one end is open so as to facethe other end of the communication hole 766 and whose other end is opento the exterior. Accordingly, the inter-piston chamber R58 cancommunicate with the exterior. Additionally, in the first housing member712, there is provided a communication hole 770 whose one end is open tothe input chamber R55 and whose other end is open to the exterior.

In the master cylinder device 702 in which the communication holes areformed thus, to the communication hole 770, an input pressure passage230 whose one end is connected to the third fluid chamber 134 of thepressure adjusting valve device 100 is connected at the other endthereof. Additionally, a pressure intensifying communication passage 684diverging from the input pressure passage 230 for supplying thepressure-adjusted brake fluid to the brake devices 56 is connected tothe antilock device 603. Also, low pressure passages 772, 774communicating with the reservoir 62 are connected to the communicationholes 762, 768, respectively.

<<Actuation of Hydraulic Brake System>>

In the hydraulic brake system 700, the input piston 710 can moveforward, according to an increase of the brake operation amount,relative to the first pressurizing piston 706 with the brake fluid inthe inter-piston chamber R58 being flowed into the reservoir 62 throughthe communication holes 760, 762 and the low pressure passage 772. Uponthe forward movement, the elastic reaction forces by the springs 736,738 increase, a forward bias force acts on the first pressurizing piston706. That is, it is possible to move the first pressurizing piston 706forward by the operation force. The seal 744 is moved forward by theforward movement of the first pressurizing piston 706, and then goesbeyond the communication hole 762 of the first housing member 712,whereby the communication between the communication hole 760 and thecommunication hole 762 is shut off. Additionally, the communication hole764 is moved forward by the forward movement of the input piston 710,and then goes beyond the seal 750 embedded in the second housing member714, whereby the communication between the communication hole 764 andthe communication hole 766 is shut off. That is, in the master cylinderdevice 702, a mechanism including the seals 744, 750 and thecommunication holes 760, 762, 764, 766 constitutes aninter-piston-chamber hermetically closing mechanism for hermeticallyclosing the inter-piston chamber R58. Also, this inter-piston-chamberhermetically closing mechanism can be considered as aninput-piston-relative-forward-movement prohibiting mechanism whichprohibits a relative forward movement of the input piston 710 relativeto the first pressurizing piston 706. Therefore, when the inter-pistonchamber R58 is hermetically closed, the operation force is transmittedvia a brake fluid in the inter-piston chamber R58 to the firstpressurizing piston 706, whereby the first pressurizing piston 706 canbe moved forward by the operation force. That is, the first pressurizingpiston 706 can be considered a pressure receiving piston whichpressurizes the brake fluid to be supplied to the brake devices 56 byreceiving the operation force or the pressure of the brake fluidsupplied to the input chamber R55. Accordingly, the master cylinderdevice 702 of the hydraulic brake system 700 is configured to realizethe operation-force/high-pressure-source-pressure dependent pressurizingstate at all times.

In this hydraulic brake system 700, master-cut valves 680, 682 areenergized to be closed in the normal condition. Accordingly, the brakefluid is not supplied from the master cylinder device 702 to the brakedevices 56 in the normal condition. Meanwhile, a pressure-intensifyingopen/close valve 686 is opened, thus the pressure-intensified brakefluid is supplied to the brake device 56 through a pressure intensifyingcommunication passage 684. Accordingly, in the brake device 56, a statein which the hydraulic brake force with a magnitude dependent on thehigh-pressure-source pressure is generated is realized in the normalcondition. Incidentally, the input piston 710 moves forward relative tothe first pressurizing piston 706 by the brake operation, and then thesprings 736, 738 generate the elastic reaction forces according to anamount of the forward movement. Therefore, a rearward bias force isapplied to the input piston 710. That is, in the master cylinder device702, a mechanism including the springs 736, 738 constitutes a reactionforce applying mechanism which applies an operation reaction forceagainst the brake operation to the input piston 710. Additionally, sincethe spring constants of the springs 736, 738 are different from eachother as described above, the master cylinder device 702 is configuredsuch that, as the operation amount of the brake pedal 70 increases, aratio of increase of the operation reaction force increases.

In the large-brake-force-required condition, the master-cut valves 680,682 are de-energized to be opened and the pressure-intensifyingopen/close valves 686FL, FR are de-energized to be closed in thehydraulic brake system 700. Therefore, the brake fluid is supplied tothe brake devices 56FL, FR from the master cylinder device 702 in theoperation-force/high-pressure-source-pressure dependent pressurizingstate, and the supply of the brake fluid from the pressure adjustingvalve device 100 is shut off. That is, in the brake devices 56FL, FR, astate in which the hydraulic brake force with a magnitude dependent onthe high-pressure-source pressure plus a hydraulic brake force with amagnitude dependent on the operation force is generated is realized inthe large-brake-force-required condition. Moreover, since the firstpressurizing piston 706 can move forward in thelarge-brake-force-required condition, the inter-piston chamber R58 ishermetically closed as described above. Therefore, the brake operationforce by the driver is transmitted to the first pressurizing piston 706without moving forward the input piston 710 relative to the firstpressurizing piston 706, that is, without generating an ineffectivebrake operation amount. Since the pressure of the brake fluids in thepressurizing chambers R3, R4 is transmitted to the input piston 710 in astate in which the hydraulic brake force with a magnitude dependent onthe high-pressure-source pressure and the operation force, the drivercan feel a rearward bias force generated by the pressure as theoperation reaction force.

In a condition in which electric power is not supplied to the hydraulicbrake system 700 due to an electric failure, each of the master-cutvalves 680, 682 and the pressure-intensifying open/close valves 686FL,FR is de-energized to come into the same open/close state as in thelarge-brake-force-required condition. However, in a case in which thebrake fluid is not supplied from the high pressure source device 58 tothe master cylinder device 702 due to an electric failure, an“operation-force dependent pressurizing state”, that is, a state inwhich the brake fluids in the pressurizing chambers R3, R4 arepressurized depending on only the operation force is realized in themaster cylinder device 702. That is, in the brake devices 56FL, FR, astate in which the hydraulic brake force with a magnitude dependent ononly the operation force is realized.

In the master cylinder device 702, the input piston 710 is not fitted tothe first pressurizing piston 706 with any seal. Therefore, even whenthe first pressurizing piston 706 is moved by the pressure of the brakefluid in the input chamber R55, no force resulting from any frictionforce of any seal acts on the input piston 710. In addition, each of thehigh-pressure seals 746, 748 between the first pressurizing piston 706and the housing 704 causes a comparatively large friction force upon amovement of the first pressurizing piston 706, whereas each of the seals750, 752 between the input piston 710 and the housing 704 causes acomparatively small friction force upon a movement of the input piston710. Therefore, in the master cylinder device 702, operational feelingin a brake operation is excellent. Especially in the operation-forcedependent pressurizing state, it is possible to provide excellentoperational feeling.

Seventh Embodiment

FIG. 10 schematically represents a hydraulic brake system 800 of theseventh embodiment. The hydraulic brake system 800 has a master cylinderdevice 802 and an antilock device 603. The hydraulic brake system 800generally has the same structure as any one of the hydraulic brakesystems of the first through sixth embodiments. In the followingdescription, with consideration for abbreviating the explanation,different construction and actuation from the hydraulic brake systemswill be described but the same construction and actuation as thehydraulic brake systems are omitted.

<<Structure of Master Cylinder Device>>

The master cylinder device 802 is categorized into the Master-Cut SystemAdoptable Type Master Cylinder Device, and has a housing 804 being acasing, a first pressurizing piston 806 and a second pressurizing piston808 which pressurize the brake fluid to be supplied to the brake devices56, an intermediate piston 810 which can move forward by the brake fluidintroduced from the high pressure source device 58, and an input piston812 to which an operation of the driver is inputted via the operationdevice 52.

The housing 804 mainly includes two members, specifically, a firsthousing member 814 and a second housing member 816. The first housingmember 814 has a roughly hollow cylindrical shape whose front end isclosed, and is sectioned into three portions having mutually differentinner diameters, specifically, a front small-diameter portion 818arranged in a front side and having a small inner diameter, a rearlarge-diameter portion 820 arranged in a rear side and having a largeinner diameter, and an intermediate portion 822 arranged between theabove two portions and having an inner diameter of a medium size betweenthe above two inner diameters. The second housing member 816 has aroughly hollow cylindrical shape whose front end has an inner flange824.

An interior of the housing 804 constructed thus is separated by theinner flange 824 of the second housing member 816 to define a front sidechamber R61 located in a front side and a rear side chamber R62 locatedin a rear side. That is, the inner flange 824 serves as a partitionportion separating the interior of the housing 804, and an innerperiphery portion of the inner flange 824 serves as an opening throughthe partition portion.

Each of the first pressurizing piston 806 and the second pressurizingpiston 808 has a hollow cylindrical shape whose rear end portion isclosed, and is slidably fitted with seals in the small-inner-diameterportion 818 of the first housing member 814 in the front side chamberR61. The intermediate piston 810 includes a front side portion 828having a hollow cylindrical shape whose front side is closed, a rearside portion 830 located in the rear of the front side portion 828 andhaving a hollow cylindrical shape, and an intermediate portion 832located between the front side portion 828 and the rear side portion 830and having a flange shape. In other words, the intermediate piston 810has a blind hole which is formed inside the front side portion 828 andthe rear side portion 830 and which is open rearward. The intermediatepiston 810 is fitted in the housing 804 with seals such that the frontside portion 828 contacts with the front small-diameter portion 818 ofthe first housing member 814, the intermediate portion 832 contacts withthe intermediate portion 822 of the first housing member 814, and therear side portion 830 contacts with the inner periphery portion of theinner flange 824 of the second housing member 816. That is, in theintermediate piston 810, the front side portion 828 and the intermediateportion 832 serves as a main body portion disposed in the front sidechamber R61, and the rear side portion 830 serves as an extensionportion extending through the inner flange 824 into the rear sidechamber R62. In addition, the first pressurizing piston 806 and theintermediate piston 810 are disposed such that there is hardly aclearance between a rear end face of the first pressurizing piston 806and a front end face of the intermediate piston 810 in no brakeoperation.

The input piston 812 has a roughly a pillar shape and is connected, at arear end thereof, to the operation rod 72. the input piston 812 isfitted in the second housing member 816 with a seal. Additionally,between a bottom face of the rearward-opening blind hole of theintermediate piston 810 and a front end face of the input piston 812,two compression coil springs 834, 836 each of which generates an elasticreaction force in a direction of separating the intermediate piston 810and the input piston 812 are disposed in series in the front-backdirection. It is noted that the spring constant of the spring 836 issmaller than the spring constant of the spring 834. Additionally,between the springs 834, 836, a floating seat 838 is disposed whilesupported by them.

In the master cylinder device 802 constructed thus, between a rear endof the intermediate portion 832 of the intermediate piston 810 and thesecond housing member 816, there is defined a fluid chamber R65 intowhich the brake fluid from the high pressure source device 58 isinputted. This fluid chamber R65 is referred to as an “input chamber”,where appropriate. It is noted that the input chamber R65 is illustratedin an almost squeezed state in FIG. 10. Additionally, between an innercircumferential face of the intermediate portion 822 of the firsthousing member 814 in front of the intermediate portion 832 and an outercircumferential face of the front side portion 828 of the intermediatepiston 810, as described below, there is defined an annular fluidchamber R66 communicating with the reservoir 62. Hereinafter, thischamber is referred to as a “breathing chamber”, where appropriate.Furthermore, between the bottom face of the rearward-open blind hole ofthe intermediate piston 810 and the input piston 812, there is formed aninter-piston chamber R68 across which the intermediate piston 810 andthe input piston 812 face to each other.

In the master cylinder device 802 in which each of the chambers isdefined thus, the input chamber R65 is defined by that the intermediatepiston 810 contacts with the intermediate portion 822 of the firsthousing member 814 via a seal 840 embedded in an outer circumferentialface of the intermediate portion 832 and contacts with an innercircumferential face of the second housing member 816 via a seal 842embedded in the inner circumferential face. By the way, the input piston812 slidably contacts with an inner circumferential face of the secondhousing member 816, and a seal 844 is embedded in an outercircumferential face of the input piston 812. It is noted that ahigh-pressure seal is employed as each of the seals 840, 842 but notemployed as the seal 844.

Additionally, in the first housing member 814, there are provided acommunication hole 860 whose one end is open to the breathing chamberR66 and whose other end is open to the exterior, and a communicationhole 862 whose one end is open to the input chamber R65 and whose otherend is open to the exterior. In the second housing member 816, there isprovided a communication hole 864 whose one end is open to theinter-piston chamber R68. Additionally, in the first housing member 814,there is provided a communication hole 866 whose one end is open so asto face the other end of the communication hole 864 and whose other endis open to the exterior. That is, the inter-piston chamber R68communicates with the exterior.

In the master cylinder device 802 in which the communication holes areformed thus, to the communication hole 862, an input pressure passage230 whose one end is connected to the third fluid chamber 134 of thepressure adjusting valve device 100 is connected at the other endthereof. Additionally, a pressure intensifying communication passage 684diverging from the input pressure passage 230 for supplying thepressure-adjusted brake fluid to the brake devices 56 is connected tothe antilock device 603. To the communication hole 860, a low pressurepassage 867 communicating with the reservoir 62 via the communicationhole 214 is connected. That is, the breathing chamber R66 is maintainedat the atmospheric pressure at all times. Additionally, to thecommunication hole 866, an external communication passage 868 divergingfrom the low pressure passage 867 is connected, and an electromagneticopen/close valve 870 which is a normally-closed valve is provided on theexternal communication passage 868. Moreover, a communication passage872 diverging from between the end connected to the communication hole866 and the open/close valve 870 in the external communication passage868 is connected to the first fluid chamber of the pressure adjustingvalve device 100 of the pressure-intensifying/reducing device 60. Thatis, in the hydraulic brake system 800, the pressure adjusting valvedevice 100 can be activated by utilizing, as the pilot pressure, not themaster pressure but the pressure of the brake fluid in the inter-pistonchamber R68.

<<Actuation of Hydraulic Brake System>>

In the hydraulic brake system 800, when the open/close valve 870 isopened, the input piston 812 can move forward according to an increaseof the brake operation amount with the brake fluid in the inter-pistonchamber R68 being flowed into the reservoir 62 through the communicationholes 864, 866 and the external communication passage 868. Upon theforward movement, the elastic reaction forces by the springs 834, 836increase, a forward bias force acts on the intermediate piston 810. Thatis, it is possible to move the first pressurizing piston 806 forward bythe operation force. In addition, when the open/close valve 870 isclosed, the inter-piston chamber R68 is hermetically closed, and theoperation force is transmitted via a brake fluid in the inter-pistonchamber R68 to the first pressurizing piston 806, whereby the firstpressurizing piston 806 can be moved forward by the operation force.That is, in the master cylinder device 802, a mechanism including theexternal communication passage 868 and the open/close valve 870constitutes an inter-piston-chamber hermetically closing mechanism whichcan hermetically close the inter-piston chamber R68. Also, thisinter-piston-chamber hermetically closing mechanism can be considered asan input-piston-relative-forward-movement prohibiting mechanism whichprohibits a relative forward movement of the input piston 812 relativeto the intermediate piston 810. That is, the first pressurizing piston806 can be considered a pressure receiving piston which pressurizes thebrake fluid to be supplied to the brake devices 56 by receiving theoperation force or the pressure of the brake fluid supplied to the inputchamber R65. Accordingly, the master cylinder device 802 of thehydraulic brake system 800 is configured to realize theoperation-force/high-pressure-source-pressure dependent pressurizingstate at all times.

In this hydraulic brake system 800, master-cut valves 680, 682 areenergized to be closed in the normal condition. Accordingly, the brakefluid is not supplied from the master cylinder device 802 to the brakedevice 58 in the normal condition. Meanwhile, the pressure-intensifyingopen/close valve 686 is opened, thus the pressure-intensified brakefluid is supplied to the brake device 58 through the pressureintensifying communication passage 684. Accordingly, in the brake device58, a state in which the hydraulic brake force with a magnitudedependent on the high-pressure-source pressure is generated is realizedin the normal condition. Incidentally, since the open/close valve 870 isenergized to be opened in the normal condition, the input piston 812moves forward relative to the intermediate piston 810 by the brakeoperation, and then the springs 834, 836 generate the elastic reactionforces according to an amount of the forward movement. Therefore, arearward bias force is applied to the input piston 812. That is, in themaster cylinder device 802, a mechanism including the springs 834, 836constitutes a reaction force applying mechanism which applies anoperation reaction force against the brake operation to the input piston812. Additionally, since the spring constants of the springs 834, 836are different from each other as described above, the master cylinderdevice 802 is configured such that, as the operation amount of the brakepedal 70 increases, a ratio of increase of the operation reaction forceincreases.

In the large-brake-force-required condition, the master-cut valves 680,682 are de-energized to be opened and the pressure-intensifyingopen/close valves 686FL, FR are de-energized to be closed in thehydraulic brake system 800. Therefore, the brake fluid is supplied tothe brake devices 56FL, FR from the master cylinder device 802 in theoperation-force/high-pressure-source-pressure dependent pressurizingstate, and the supply of the brake fluid from the pressure adjustingvalve device 100 is shut off. That is, in the brake devices 56FL, FR, astate in which the hydraulic brake force with a magnitude dependent onthe high-pressure-source pressure plus a hydraulic brake force with amagnitude dependent on the operation force is generated is realized inthe large-brake-force-required condition. In thelarge-brake-force-required condition, the open/close valve 870 is alsode-energized to be closed, thereby hermetically closing the inter-pistonchamber R68. Therefore, the brake operation force by the driver istransmitted to the intermediate piston 810 and the first pressurizingpiston 806 without moving forward the input piston 812 relative to thefirst pressurizing piston 810, that is, without generating anineffective brake operation amount. Since the pressure of the brakefluids in the pressurizing chambers R3, R4 is transmitted to the inputpiston 812 in the operation-force/high-pressure-source-pressuredependent pressurizing state, the driver can feel a rearward bias forcegenerated by the pressure as the operation reaction force.

In a condition in which electric power is not supplied to the hydraulicbrake system 800 due to an electric failure, each of the master-cutvalves 680, 682, the pressure-intensifying open/close valves 686FL, FR,and the open/close valve 870 is de-energized to come into the sameopen/close state as in the large-brake-force-required condition.However, in a case in which the brake fluid is not supplied from thehigh pressure source device 58 to the master cylinder device 802 due toan electric failure, an “operation-force dependent pressurizing state”,that is, a state in which the brake fluids in the pressurizing chambersR3, R4 are pressurized dependent on only the operation force is realizedin the master cylinder device 802. That is, in the brake devices 56FL,FR, a state in which the hydraulic brake force with a magnitudedependent on only the operation force is realized. That is, in thehydraulic brake system 800, when an electric failure etc. occurs, thepressure adjusting valve device 100 can be activated by utilizing thepressure of the brake fluid in the inter-piston chamber R68 as the pilotpressure. Therefore, unlike utilizing, as the pilot pressure, the masterpressure which is affected by a friction force etc. upon a movement ofthe first pressurizing piston 806, the activation of the pressureadjusting valve device 100 is comparatively favorable in an ability offollowing a change of brake operation.

In the master cylinder device 802, the input piston 812 is not fitted tothe intermediate piston 810 with any seal. Therefore, even when theintermediate piston 810 is moved by the pressure of the brake fluid inthe input chamber R65, no force resulting from any friction force of anyseal acts on the input piston 812. In addition, each of thehigh-pressure seals 840, 842 between the intermediate piston 810 and thehousing 804 causes a comparatively large friction force upon a movementof the intermediate piston 810, whereas the seal 844 between the inputpiston 812 and the housing 804 causes a comparatively small frictionforce upon a movement of the input piston 812. Therefore, in the mastercylinder device 802, operational feeling in a brake operation isexcellent. Especially in the operation-force dependent pressurizingstate, it is possible to provide excellent operational feeling.

Eighth Embodiment

FIG. 11 schematically represents a hydraulic brake system 900 of theeighth embodiment. The hydraulic brake system 900 has a master cylinderdevice 902 and an antilock device 54. The hydraulic brake system 900generally has the same structure as any one of the hydraulic brakesystems of the first through seventh embodiments. In the followingdescription, with consideration for abbreviating the explanation,different construction and actuation from the hydraulic brake systemswill be described but the same construction and actuation as thehydraulic brake systems are omitted.

<<Structure of Master Cylinder Device>>

The master cylinder device 902 is categorized into the PressureReceiving Piston Lock Type Master Cylinder Device, and has a housing 904being a casing, a first pressurizing piston 906 and a secondpressurizing piston 908 which pressurize the brake fluid to be suppliedto the brake devices 56, an intermediate piston 910 which can moveforward by the brake fluid introduced from the high pressure sourcedevice 58, and an input piston 912 to which an operation of the driveris inputted via the operation device 52.

The housing 904 mainly includes two members, specifically, a firsthousing member 914 and a second housing member 916. The first housingmember 914 has a roughly hollow cylindrical shape whose front end isclosed, and is sectioned into three portions having mutually differentinner diameters, specifically, a front small-diameter portion 918arranged in a front side and having a small inner diameter, a rearlarge-diameter portion 920 arranged in a rear side and having a largeinner diameter, and an intermediate portion 922 arranged between theabove two portions and having an inner diameter of a medium size betweenthe above two inner diameters. The second housing member 916 has aroughly hollow cylindrical shape whose front end has an inner flange924. The first housing member 914 and the second housing member 916 areunited in a state in which a front end face of the second housing member916 abuts on a stepping face between the intermediate portion 922 andthe rear large-diameter portion 920 of the first housing member 914.

An interior of the housing 904 constructed thus is separated by theinner flange 924 of the second housing member 916 to define a front sidechamber R71 located in a front side and a rear side chamber R72 locatedin a rear side. That is, the inner flange 924 serves as a partitionportion separating the interior of the housing 904, and an innerperiphery portion 924 serves as an opening through the partitionportion.

Each of the first pressurizing piston 906 and the second pressurizingpiston 908 has a hollow cylindrical shape whose rear end portion isclosed, and is slidably fitted with seals in the small-inner-diameterportion 918 of the first housing member 914 in the front side chamberR71. The intermediate piston 910 roughly has a hollow cylindrical shapewhose front end portion is closed, that is, a shape having a blind holebeing open rearward, and is sectioned into a front side portion 928arranged in a front side and a rear side portion 930 arranged in a rearside. In addition, a flange 932 is formed on a rear end of the frontside portion 928. The intermediate piston 910 is fitted in the housing904 with seals such that the front side portion 928 contacts with thefront small-diameter portion 918 of the first housing member 914, theflange 932 contacts with the intermediate portion 922 of the firsthousing member 914, and the rear side portion 930 contacts with theinner periphery portion of the inner flange 924 of the second housingmember 916. That is, in the intermediate piston 910, the front sideportion 928 is considered a main body portion disposed in the front sidechamber R71, while the rear side portion 930 can be considered anextension portion extending through the opening defined by the innerflange 924 into the rear side chamber R72. In addition, the firstpressurizing piston 906 and the intermediate piston 910 are disposedsuch that a front end face of the intermediate piston 910 abuts on arear end face of the first pressurizing piston 906 in no brakeoperation.

The input piston 912 has a roughly a solid cylindrical shape having astepping portion due to a difference of an outer diameter thereof, andis connected, at a rear end thereof, to an operation rod 72. The inputpiston 912 is fitted in the rear side chamber R72, that is, the secondhousing member 916 with seals. Additionally, between a bottom face ofthe rearward-opening blind hole of the intermediate piston 910 and afront end face of the input piston 912, two compression coil springs934, 936 each of which generates an elastic reaction force in adirection of separating the intermediate piston 910 and the input piston912 are disposed in series in the front-back direction. It is noted thatthe spring constant of the spring 936 is smaller than the springconstant of the spring 934. Additionally, between the springs 934, 936,a floating seat 938 is disposed such that it is supported by them.

In the master cylinder device 902 constructed thus, between the rear endface of the first pressurizing portion 906 and the front end face of theintermediate piston 910, there is defined a fluid chamber R74 into whichthe brake fluid from the high pressure source device 58 is inputted.This fluid chamber R74 is referred to as a “first input chamber”, whereappropriate. Also, between a rear end of the front side portion 928 ofthe intermediate piston 910 and the inner flange 924 of the secondhousing member 916, there is defined a fluid chamber R75 into which thebrake fluid from the high pressure source device 58 is inputted. Thisfluid chamber R75 is referred to as a “second input chamber”, whereappropriate. It is noted that each of the input chambers R74, R75 isillustrated in an almost squeezed state in FIG. 11. Additionally,between an inner circumferential face of the intermediate portion 922 ofthe first housing member 914 in front of the flange 932 and an outercircumferential face of the front side portion 928 of the intermediatepiston 910, as described below, there is defined an annular fluidchamber R76 which opposes the second input chamber R75 with the flange932 being interposed between the fluid chamber R76 and the second inputchamber and which can communicate with the reservoir 62. Hereinafter,this chamber is referred to as an “opposing chamber”, where appropriate.Additionally, in the intermediate piston 910, a pressurized area onwhich a pressure of a brake fluid in the first input chamber R74 acts,namely, an area of a front end face of the front side portion 928, and apressurized area on which a pressure of a brake fluid in the secondinput chamber R75 acts, namely, an area of a rear end face of the flange932 are equal. Furthermore, between the bottom face of the rearward-openblind hole of the intermediate piston 910 and a front end face of theinput piston 912, there is formed an inter-piston chamber R78 acrosswhich the intermediate piston 910 and the input piston 912 face to eachother.

In the master cylinder device 902 in which each of the chambers isdefined thus, the intermediate piston 910 contacts with the front sideportion 918 of the first housing member 914 via seals 940, 942 embeddedin the front side portion 928. Additionally, the second input chamberR75 is defined by that the intermediate piston 910 contacts with theintermediate portion 922 of the first housing member 914 via a seal 944embedded in an outer circumferential face of the flange 932 and contactswith an inner circumferential face of the inner flange 924 of the secondhousing member 916 via a seal 946 embedded in the inner circumferentialface. In addition, the input piston 912 slidably contacts with an innercircumferential face of the second housing member 916. Therefore, a seal948 is embedded in an outer circumferential face of the input piston912, and a seal 950 is embedded in a rear end portion of the secondhousing member 916. It is noted that a high-pressure seal is employed aseach of the seals 944, 946 but not employed as each of the seals 948,950.

Between an outer circumferential face of the first pressurizing piston906 and the inner circumferential face of the front small-diameterportion 918 of the first housing member 914, there is provided a fluidpassage 960 having a certain cross section area through which the brakefluid can flow and connected to the first input chamber R74. In thefirst housing member 914, there is provided a communication hole 962whose one end is open to the fluid passage 960 and whose other end isopen to the exterior. That is, the first input chamber R74 communicateswith the exterior. Additionally, in the first housing member 914, thereare provided a communication hole 964 whose one end is open to theopposing chamber R76 and whose other end is open to the exterior, and acommunication hole 966 whose one end is open to the second input chamberR75 and whose other end is open to the exterior. In the intermediatepiston 910, there is provided a communication hole 968 whose one end isopen to the inter-piston chamber R78 and whose other end is open betweenthe seal 940 and the seal 942. Additionally, in the first housing member914, there is provided a communication hole 970 whose one end is open soas to face the other end of the communication hole 968 and whose otherend is open to the exterior. Accordingly, the inter-piston chamber R78can communicate with the exterior. Since an outer diameter of a part ofthe second housing member 916 is slightly smaller than an inner diameterof the rear large-diameter portion 920 of the first housing member 914,there is defined a fluid passage 972 having a certain cross section areathrough which the brake fluid can flow. In the second housing member916, there is provided a communication hole 974 whose one end is open tothe fluid passage 972 and whose other end is open in the rear of thestepping portion of the input piston 912. In the first housing member914, there is provided a communication hole 976 whose one end is open tothe fluid passage 972 and whose other end is open to the exterior.

In the master cylinder device 902 in which the fluid passages and thecommunication holes are formed thus, to the communication hole 966, aninput pressure passage 230 whose one end is connected to the third fluidchamber 134 of the pressure adjusting valve device 100 is connected atthe other end thereof. Also, an input pressure passage 980 divergingfrom an input pressure passage 230 is connected to the communicationhole 962. To the communication hole 964, a low pressure passage 982communicating with the reservoir 62 is connected, and an electromagneticopen/close valve 984 which is a normally-opened valve is provided on thelow pressure passage 982. Therefore, the opposing chamber R76 cancommunicate with the reservoir 62, thus a mechanism including theopen/close valve 984 and the low pressure passage 982 constitutes alow-pressure-source communication mechanism which allows the opposingchamber R76 to communicate with the reservoir 62. Also, an externalcommunication passage 986 communicating with the reservoir 62 isconnected to the communication hole 970. Moreover, an externalcommunication passage 988 communicating with the reservoir 62 isconnected to the communication hole 976. Accordingly, a space in therear of the stepping portion of the input piston 912 is maintained atthe atmospheric pressure at all times

<<Actuation of Hydraulic Brake System>>

As described above, in the intermediate piston 910, since thepressurized area on which the pressure of the brake fluid in the firstinput chamber R74 acts and the pressurized area on which the pressure ofa brake fluid in the second input chamber R75 acts are almost equal, nomovement of the intermediate piston 910, or a slight movement if any,occurs depending on the pressures of the brake fluids in the first inputchamber R74 and the second input chamber R75. Additionally, in thenormal condition, since the open/close valve 984 is closed tohermetically close the opposing chamber R76, a forward movement of theintermediate piston 910 is prohibited. When a brake operation isperformed, the input piston 912 can move forward with the brake fluid inthe inter-piston chamber R78 being flowed into the reservoir 62 throughthe communication holes 968, 970 and the external communication passage986. That is, in the normal condition, a relative forward movement ofthe input piston 912 to the intermediate piston 910 is allowed. By theway, a mechanism including the springs 934, 936 serves as a reactionforce applying mechanism which applies the operation reaction force to adriver by an increase of the elastic reaction force due to the relativeforward movement. Additionally, since the spring constants of thesprings 934, 936 are different from each other as described above, themaster cylinder device 902 is configured such that, as the operationamount of the brake pedal 70 increases, a ratio of increase of theoperation reaction force increases. Meanwhile, in the normal condition,the first pressurizing piston 906 is moved forward depending on thepressure of the brake fluid in the first pressurizing piston R74. Thatis, in the normal condition, a high-pressure-source-pressure dependentpressurizing state in which the brake fluid in the pressurizing chambersR3, R4 can be pressurized depending on only the pressure of the brakefluid in the first input chamber R74 is realized. So to say, in themaster cylinder device 902, the high-pressure-source-pressure dependentpressurizing state is realized by fixing (locking) the intermediatepiston 910.

In the large-brake-force-required condition, the open/close valve 984 isde-energized to be opened, thereby allowing the forward movement of theintermediate piston 910. Accordingly, the intermediate piston 910 canmove forward by a force according to the pressure of the brake fluidsupplied to the second input chamber R75. Since the intermediate piston910 abuts on the first pressurizing piston 906, the intermediate piston910 moves the pressurizing pistons 906, 908 forward to pressurize thebrake fluid to be supplied to the brake devices 56. In addition, since aforward bias force acts on the intermediate piston 910 due to theelastic reaction forces by the springs 934, 936 on a brake operation,the intermediate piston 910 is moved by the operation force as well.That is, the pressurizing pistons 906, 908 can move forward depending onnot only the pressure of the brake fluid in the second input chamber R75but also the operation force, whereby the brake fluids in thepressurizing chambers R3, R4 are pressurized. Accordingly, in the mastercylinder device 902, the operation-force/high-pressure-source-pressuredependent pressurizing state is realized in thelarge-brake-force-required condition. Therefore, the intermediate piston910 can be considered a pressure receiving piston which pressurizes thebrake fluid to be supplied to the brake devices 56 by receiving theoperation force or the pressure of the brake fluid supplied to thesecond input chamber R75.

Additionally, the seal 942 disposed behind the communication hole 968formed in the intermediate piston 910 is moved forward by the forwardmovement of the intermediate piston 910, and then goes beyond theopening of the communication hole 970 formed in the first housing member914, whereby the communication between the communication hole 968 andthe communication hole 970 is shut off. Accordingly, the inter-pistonchamber R78 is hermetically closed, and then the operation force can betransmitted, via the brake fluid in the inter-piston chamber R78, to thefirst pressurizing piston 906. That is, in the master cylinder device902, a mechanism including the communication holes 968, 970 constitutesan inter-piston-chamber hermetically closing mechanism which canhermetically close the inter-piston chamber R78. Also, thisinter-piston-chamber hermetically closing mechanism can be considered asan input-piston-relative-forward-movement prohibiting mechanism whichprohibits a relative forward movement of the input piston 912 relativeto the intermediate piston 910. Therefore, the brake operation force bythe driver is transmitted to the intermediate piston 910 and the firstpressurizing piston 906 without generating an ineffective brakeoperation amount. Incidentally, in theoperation-force/high-pressure-source-pressure dependent pressurizingstate, since the pressure of the brake fluids in the pressurizingchambers R3, R4 is transmitted to the input piston 912, the driver canfeel the rearward bias force generated by the pressure as the operationreaction force.

In a condition in which electric power is not supplied to the hydraulicbrake system 900 due to an electric failure, since the open/close valve984 is de-energized to be opened, the forward movement of theintermediate piston 910 is allowed as in the large-brake-force-requiredcondition, whereby the pressurizing pistons 906, 908 can be movedforward by the operation force. That is, in the master cylinder device902, it is possible to pressurize the brake fluids in the pressurizingchambers R3, R4 depending on only the operation force so as to supplythe brake fluid to the brake devices 56FL, 56FR. That is, in the mastercylinder device 902, the operation-force dependent pressurizing state isrealized. Incidentally, when the pressure-intensified brake fluid isstored in the accumulator 92 of the high pressure source device 58, thepressure of the pressure-intensified brake fluid assists thepressurizing of the brake fluids in the pressurizing chambers R3, R4.

In the master cylinder device 902, the input piston 912 is not fitted tothe intermediate piston 910 with any seal. Therefore, even when theintermediate piston 910 is moved by the pressure of the brake fluid inthe second input chamber R75, no force resulting from any friction forceof any seal acts on the input piston 912. In addition, each of thehigh-pressure seals 944, 946 between the intermediate piston 910 and thehousing 904 causes a comparatively large friction force upon a movementof the intermediate piston 910, whereas each of the seals 948, 950between the input piston 912 and the housing 904 causes a comparativelysmall friction force upon a movement of the input piston 912. Therefore,in the master cylinder device 902, operational feeling in a brakeoperation is excellent especially in the operation-force dependentpressurizing state. So it is possible to provide excellent operationalfeeling especially in the operation-force dependent pressurizing state.

Ninth Embodiment

FIG. 12 schematically represents a hydraulic brake system 1000 of theninth embodiment. The hydraulic brake system 1000 has a master cylinderdevice 1002 and an antilock device 54. The hydraulic brake system 1000generally has the same structure as any one of the hydraulic brakesystems of the first through eighth embodiments. In the followingdescription, with consideration for abbreviating the explanation,different construction and actuation from the hydraulic brake systemswill be described but the same construction and actuation as thehydraulic brake systems are omitted.

<<Structure of Master Cylinder Device>>

The master cylinder device 1002 is categorized into the PressureReceiving Piston Lock Type Master Cylinder Device, and has a housing1004 being a casing, a first pressurizing piston 1006 and a secondpressurizing piston 1008 which pressurize the brake fluid to be suppliedto the brake devices 56, an intermediate piston 1010 which can moveforward by the brake fluid introduced from the high pressure sourcedevice 58, and an input piston 1012 to which an operation of the driveris inputted via the operation device 52.

The housing 1004 mainly includes two members, specifically, a firsthousing member 1014 and a second housing member 1016. The first housingmember 1014 has a roughly hollow cylindrical shape whose front end isclosed, and is sectioned into three portions having mutually differentinner diameters, specifically, a small-diameter portion 1018 arranged ina front side and having a small inner diameter, a large-diameter portion1020 arranged in a rear side and having a large inner diameter, and anintermediate portion 1022 arranged between the above two portions andhaving an inner diameter of a medium size between the above two innerdiameters. The second housing member 1016 has a roughly hollowcylindrical shape, and is sectioned into two portions having mutuallydifferent outer diameters, specifically, a small-outer-diameter portion1024 arranged in a front side and having a small inner diameter, and alarge-outer-diameter portion 1026 arranged in a rear side and having alarge inner diameter. The second housing member 1016 is united with thefirst housing member 1016 in a state in which the second housing member1016 is inserted in the first housing member 1014 from the rear side.

In the housing 1004 constructed above, a front end portion of thelarge-outer-diameter portion 1026 of the second housing member 1016serves an annular separation wall portion projecting to the inside in aradial direction, and the small-outer-diameter portion 1024 serves aninner cylindrical portion extending forward from an inner periphery ofthe separation wall portion, In other words, in the housing 1004, apartition portion separating an interior of the housing 1004 is formedby the small-outer-diameter portion 1024 and the large-outer-diameterportion 1026 of the second housing member 1016. Therefore, the interiorof the housing 1004 is separated into a front side chamber R81 includinga space outside the small-outer-diameter portion 1024 and a rear sidechamber R82 including an inside space of the small-outer-diameterportion 1024. In addition, a front end of the small-outer-diameterportion 1024 serves as an opening formed in the partition portion.

Each of the first pressurizing piston 1006 and the second pressurizingpiston 1008 has a hollow cylindrical shape whose rear end portion isclosed, and is slidably fitted with seals in the small-inner-diameterportion 1018 of the first housing member 1014 in the front side chamberR81. The intermediate piston 1010 roughly has a hollow cylindrical shapewhose front end portion is closed, that is, a shape having a blind holebeing open rearward, and includes a main body portion 1028 having ahollow cylindrical shape. A flange 1030 is formed on an outer peripheryof a rear end of the main body portion 1028. The intermediate piston1010 is fitted with seals in the housing 1004 such that a front portionof the main body portion 1028 slidably contacts with thesmall-inner-diameter portion 1018 of the first housing member 1014, theflange 1030 slidably contacts with the intermediate portion 1022, and aninner circumferential portion of the main body portion 1028 slidablycontacts with the small-outer-diameter portion 1024 of the secondhousing member 1016. That is, the intermediate piston 1010 is disposedsuch that the small-outer-diameter portion 1024 of the second housingmember 1016 is inserted in the main body portion 1028, in other words,such that the main body portion 1028 is interposed between theintermediate portion 1022 of the first housing member 1014 and thesmall-outer-diameter portion 1024 of the second housing member 1016. Soto speak, the intermediate portion 1022 of the first housing member 1014can be considered to be an outer cylindrical portion of the housing1004. In addition, the first pressurizing piston 1006 and theintermediate piston 1010 are disposed such that a front end face of theintermediate piston 1010 abuts on a rear end face of the firstpressurizing piston 1006 in no brake operation.

The input piston 1012 includes a base end portion 1032 to which theoperation rod 72 is connected, a rod portion 1034 screwed in the baseend portion 1032 and extending forward from the base end portion 1032,and a movable portion 1036 slidably fitted to the rod portion 1034. Inthe input piston 1012, a rearward movement of the movable portion 1036relative to the base end portion 1032, in other words, a shrink of theinput piston 1012 is allowed. Additionally, between the base end portion1032 and the movable portion 1036, two compression coil springs 1038,1040 each of which generates an elastic reaction force for biasing themovable portion 1036 forward are disposed in series in the front-backdirection. It is noted that the spring constant of the spring 1040 issmaller than the spring constant of the spring 1038. Additionally,between the springs 1038, 1040, a floating seat 1042 is disposed suchthat it is supported by them and the rod portion 1034 passes through thefloating seat 1042. Incidentally, a flange is provided on an outerperiphery of a front end portion of the rod portion 1034, and the flangeprevents the movable portion 1036 from coming out forward from the rodportion 1034. The input piston 1012 is fitted with seals in an inside ofthe second housing member 1016 with the movable portion 1036 beinginserted in the small-outer-diameter portion 1024 of the second housingmember 1016. That is, the input piston 1012 is disposed such that thefront side thereof is located in the main body portion 1028 of theintermediate piston 1010. Accordingly, in the master cylinder device1002, since a part of the intermediate piston 1010 and a part of theinput piston 1012 overlap with each other in the front-back direction,the entire length of the master cylinder device 1002 is comparativelyshort.

In the master cylinder device 1002 constructed thus, between the rearend face of the first pressurizing portion 1006 and the front end faceof the intermediate piston 1010, there is defined a fluid chamber R84into which the brake fluid from the high pressure source device 58 isinputted. This fluid chamber R84 is referred to as a “first inputchamber”, where appropriate. Also, between a rear end of the flange 1030of the intermediate piston 1010 and a stepping face, which is formedbetween the small-outer-diameter portion 1024 and thelarge-outer-diameter portion 1026 of the second housing member 1016,there is defined another fluid chamber R85 into which the brake fluidfrom the high pressure source device 58 is inputted. This fluid chamberR85 is referred to as a “second input chamber”, where appropriate. It isnoted that each of the input chambers R84, R85 is illustrated in analmost squeezed state in FIG. 12. Additionally, between an innercircumferential face of the intermediate portion 1022 of the firsthousing member 1014 in front of the flange 1030 and an outercircumferential face of the front side portion 1028 of the intermediatepiston 1010, as described below, there is defined an annular fluidchamber R86 which opposes the second input chamber with the flange 1030being interposed between the fluid chamber R86 and the second inputchamber and which can communicate with the reservoir 62. Hereinafter,this chamber is referred to as an “opposing chamber”, where appropriate.Additionally, in the intermediate piston 1010, a pressurized area onwhich a pressure of a brake fluid in the first input chamber R84 acts,namely, an area of a front end face of the front side portion 1028, anda pressurized area on which a pressure of a brake fluid in the secondinput chamber R85 acts, namely, an area of a rear end face of the flange1030 are equal. Moreover, inside the input piston 1012, a fluid chamber(hereinafter, referred to as an “internal chamber”, where appropriate)R87 for allowing a shrink of the input piston 1012 is defined betweenthe base end portion 1032 and the movable portion 1036. Furthermore,between the bottom face of the rearward-open blind hole of theintermediate piston 1010 and a forward-facing face of the input piston1012, there is formed an inter-piston chamber R88 across which theintermediate piston 1010 and the input piston 1012 face to each other.

In the master cylinder device 1002 in which each of the chambers isdefined thus, the second input chamber R85 is defined by that theintermediate piston 1010 contacts with an inner circumferential face ofthe intermediate portion 1022 of the first housing member 1014 via aseal 1044 embedded in an outer circumferential face of the flange 1030and contacts with an outer circumferential face of thesmall-outer-diameter portion 1024 of the second housing member 1016 viaa seal 1046 embedded in an inner circumferential face of the main bodyportion 1028. In addition, the input piston 1012 slidably contacts withthe inner circumferential face of the second housing member 1016.Therefore, a seal 1048 is embedded in an outer circumferential face ofthe base end portion 1032, and a seal 1050 is embedded in an outercircumferential face of the movable portion 1036. It is noted that ahigh-pressure seal is employed as each of the seals 1044, 1046 but notemployed as each of the seals 1048, 1050.

Between an outer circumferential face of the first pressurizing piston1006 and an inner circumferential face of the small-inner-diameterportion of the first housing member 1014, there is provided a fluidpassage 1060 having a certain cross section area through which the brakefluid can flow and connected to the first input chamber R84. In thefirst housing member 1014, there is provided a communication hole 1062whose one end is open to the fluid passage 1060 and whose other end isopen to the exterior. That is, the first input chamber R84 communicateswith the exterior. Additionally, in the first housing member 1014, thereare provided a communication hole 1064 whose one end is open to theopposing chamber R86 and whose other end is open to the exterior, and acommunication hole 1066 whose one end is open to the second inputchamber R85 and whose other end is open to the exterior. In the secondhousing member 1016, there is provided a communication hole 1068 whoseone end is open to the internal chamber R87. Additionally, in the firsthousing member 1014, there is provided a communication hole 1070 whoseone end is open so as to face the other end of the communication hole1068 and whose other end is open to the exterior. That is, the internalchamber R87 communicates with the exterior.

In the master cylinder device 1002 in which the fluid passages and thecommunication holes are formed thus, to the communication hole 1066, aninput pressure passage 230 whose one end is connected to the third fluidchamber 134 of the pressure adjusting valve device 100 is connected atthe other end thereof. Also, an input pressure passage 1080 divergingfrom an input pressure passage 230 is connected to the communicationhole 1062. To the communication hole 1064, a low pressure passage 1082communicating with the reservoir 62 is connected, and an electromagneticopen/close valve 1084 which is a normally-opened valve is provided onthe low pressure passage 1082. Therefore, the opposing chamber R86 cancommunicate with the reservoir 62, thus a mechanism including theopen/close valve 1084 and the low pressure passage 1082 constitutes alow-pressure-source communication mechanism which allows the opposingchamber R86 to communicate with the reservoir 62. Additionally, to thecommunication hole 1070, an external communication passage 1086communicating with the reservoir 62 is connected, and an electromagneticopen/close valve 1088 which is a normally-closed valve is provided onthe external communication passage 1086.

<<Actuation of Hydraulic Brake System>>

As described above, in the intermediate piston 1010, since thepressurized area on which the pressure of the brake fluid in the firstinput chamber R84 acts and the pressurized area on which the pressure ofa brake fluid in the second input chamber R85 acts are almost equal, nomovement of the intermediate piston 1010, or a slight movement if any,occurs depending on the pressures of the brake fluids in the first inputchamber R84 and the second input chamber R85. Additionally, in thenormal condition, since the open/close valve 1084 is closed tohermetically close the opposing chamber R86, a forward movement of theintermediate piston 1010 is prohibited. However, in the normalcondition, the open/close valve 1088 is opened, whereby the internalchamber R87 communicates with the reservoir 62. Therefore, when a brakeoperation is performed, the base end portion 1032 and the rod portion1034 of the input piston 1012 can move forward with the brake fluid inthe internal chamber R87 being flowed into the reservoir 62.Accordingly, in the normal condition, a relative forward movement of theinput piston 1012 to the intermediate piston 1010 is allowed. Meanwhile,in the normal condition, the first pressurizing piston 1006 is movedforward depending on the pressure of the brake fluid in the firstpressurizing piston R84. That is, in the normal condition, ahigh-pressure-source-pressure dependent pressurizing state in which thebrake fluid in the pressurizing chambers R3, R4 can be pressurizeddepending on only the pressure of the brake fluid in the first inputchamber R84 is realized. In this state, even though the rod portion 1034of the input piston 1012 moves forward, a volume of the brake fluid inthe inter-piston chamber R88 cannot change. Therefore, the movableportion 1036 moves rearward by a degree corresponding to the forwardmovement of the rod portion 1034. Consequently, the elastic reactionforces of the springs 1038, 1040 increase, whereby a driver can feel anincrease of the operation reaction force against the increase of thebrake operation amount by the driver. That is, a mechanism including thesprings 1038, 1040 serves as a reaction force applying mechanism whichapplies the operation reaction force to a driver. Additionally, sincethe spring constants of the springs 1038, 1040 are different from eachother as described above, the master cylinder device 1002 is configuredsuch that, as the operation amount of the brake pedal 70 increases, aratio of increase of the operation reaction force increases.

In the large-brake-force-required condition, the open/close valve 1084is de-energized to be opened, thereby allowing the forward movement ofthe intermediate piston 1010 in the hydraulic brake system 1000.Accordingly, the intermediate piston 1010 can move forward by a forceaccording to the pressure of the brake fluid in the second input chamberR85. Since the intermediate piston 1010 abuts on the first pressurizingpiston 1006, the intermediate piston 1010 moves the pressurizing pistons1006, 1008 forward to pressurize the brake fluid to be supplied to thebrake devices 56. In addition, since a pressure of the brake fluid inthe inter-piston chamber R88 increases due to the elastic reactionforces by the springs 1038, 1040, a forward bias force acts on theintermediate piston 1010. Accordingly, the intermediate piston 1010 ismoved by the operation force as well. That is, the pressurizing pistons1006, 1008 can move forward depending on not only the pressure of thebrake fluid in the second input chamber R85 but also the operationforce, whereby the brake fluids in the pressurizing chambers R3, R4 arepressurized. Accordingly, in the master cylinder device 1002, theoperation-force/high-pressure-source-pressure dependent pressurizingstate is realized in the large-brake-force-required condition.Therefore, the intermediate piston 1010 can be considered a pressurereceiving piston which pressurizes the brake fluid to be supplied to thebrake devices 56 by receiving the operation force or the pressure of thebrake fluid supplied to the second input chamber R85.

In the large-brake-force-required condition, the open/close valve 1088is also de-energized to be closed. Accordingly, the internal chamber R87is hermetically closed, the operation force can be transmitted, via thebrake fluid in the internal chamber R87, to the first pressurizingpiston 1006. That is, in the master cylinder device 1002, a mechanismincluding the external communication passage 1086 and the open/closevalve 1088 constitutes an input-piston-relative-forward-movementprohibiting mechanism which prohibits the relative forward movement ofthe input piston 1012 to the intermediate piston 1010. Therefore, thebrake operation force by the driver is transmitted to the intermediatepiston 1010 and the first pressurizing piston 1006 without generating anineffective brake operation amount. Incidentally, in theoperation-force/high-pressure-source-pressure dependent pressurizingstate, since the pressure of the brake fluids in the pressurizingchambers R3, R4 is transmitted to the input piston 1012, the driver canfeel the rearward bias force generated by the pressure as the operationreaction force.

In a condition in which electric power is not supplied to the hydraulicbrake system 1000 due to an electric failure, since the open/close valve1084 is de-energized to be opened, the forward movement of theintermediate piston 1010 is allowed as in the large-brake-force-requiredcondition, whereby the pressurizing pistons 1006, 1008 can be movedforward by the operation force. That is, in the master cylinder device1002, it is possible to pressurize the brake fluids in the pressurizingchambers R3, R4 depending on only the operation force so as to supplythe brake fluid to the brake devices 56FL, 56FR. That is, in the mastercylinder device 1002, the operation-force dependent pressurizing stateis realized. Additionally, in an electric failure, the open/close valve1088 is de-energized to be closed, thus the internal chamber R87 ishermetically closed. Therefore, the brake operation force by the driveris transmitted to the pressurizing pistons 1006, 1008 without generatingan ineffective brake operation amount.

In the master cylinder device 1002, the input piston 1012 is not fittedto the intermediate piston 1010 with any seal. Therefore, even when theintermediate piston 1010 is moved by the pressure of the brake fluid inthe second input chamber R85, no force resulting from any friction forceof any seal acts on the input piston 1012. In addition, each of thehigh-pressure seals 1044, 1046 between the intermediate piston 1010 andthe housing 1004 causes a comparatively large friction force upon amovement of the intermediate piston 1010, whereas each of the seals1048, 1050 between the input piston 1012 and the housing 1004 causes acomparatively small friction force upon a movement of the input piston1012. Therefore, in the master cylinder device 1002, operational feelingin a brake operation is excellent. Especially in the operation-forcedependent pressurizing state, it is possible to provide excellentoperational feeling.

Tenth Embodiment

FIG. 13 schematically represents a hydraulic brake system 1100 of thetenth embodiment. The hydraulic brake system 1100 has a master cylinderdevice 1102 and an antilock device 54. The hydraulic brake system 1100generally has the same structure as any one of the hydraulic brakesystems of the first through ninth embodiments. In the followingdescription, with consideration for abbreviating the explanation,different construction and actuation from the hydraulic brake systemswill be described but the same construction and actuation as thehydraulic brake systems are omitted.

<<Structure of Master Cylinder Device>>

The master cylinder device 1102 is categorized into the PressureReceiving Piston Lock Type Master Cylinder Device, and has a housing1104 being a casing, a first pressurizing piston 1106 and a secondpressurizing piston 1108 which pressurize the brake fluid to be suppliedto the brake devices 56, an intermediate piston 1110 which can moveforward by the brake fluid introduced from the high pressure sourcedevice 58, and an input piston 1112 to which an operation of the driveris inputted via the operation device 52.

The housing 1104 mainly includes two members, specifically, a firsthousing member 1114 and a second housing member 1116. The first housingmember 1114 has a roughly hollow cylindrical shape whose front end isclosed, and is sectioned into three portions having mutually differentinner diameters, specifically, a small-inner-diameter portion 1118arranged in a front side and having a small inner diameter, alarge-inner-diameter portion 1120 arranged in a rear side and having alarge inner diameter, and an intermediate portion 1122 arranged betweenthe above two portions and having an inner diameter of a medium sizebetween the above two inner diameters. The second housing member 1116has a roughly hollow cylindrical shape, and is sectioned into twoportions having mutually different outer diameters, specifically, asmall-outer-diameter portion 1124 arranged in a front side and having asmall inner diameter, and a large-outer-diameter portion 1126 arrangedin a rear side and having a large inner diameter.

In the housing 1104 constructed above, a front end portion of thelarge-outer-diameter portion 1126 of the second housing member 1116serves an annular separation wall portion projecting to the inside in aradial direction, and the small-outer-diameter portion 1124 serves aninner cylindrical portion extending forward from an inner periphery ofthe separation wall portion, In other words, in the housing 1104, apartition portion separating an interior of the housing 1104 is formedby the small-outer-diameter portion 1124 and the large-outer-diameterportion 1126 of the second housing member 1116. Therefore, the interiorof the housing 1104 is separated into a front side chamber R91 includinga space outside the small-outer-diameter portion 1124 and a rear sidechamber R92 including an inside space of the small-outer-diameterportion 1124. In addition, a front end of the small-outer-diameterportion 1124 serves as an opening formed in the partition portion.

Each of the first pressurizing piston 1106 and the second pressurizingpiston 1108 has a hollow cylindrical shape whose rear end portion isclosed, and is slidably fitted with seals in the small-inner-diameterportion 1118 of the first housing member 1114 in the front side chamberR91. The intermediate piston 1110 roughly has a hollow cylindrical shapewhose front end portion is closed, that is, a shape having a blind holebeing open rearward, and includes a main body portion 1128 having ahollow cylindrical shape. A flange 1130 is formed on an outer peripheryof a rear end of the main body portion 1128. The intermediate piston1110 is fitted with seals in the housing 1104 such that a front portionof the main body portion 1128 slidably contacts with thesmall-inner-diameter portion 1118 of the first housing member 1114, theflange 1130 slidably contacts with the intermediate portion 1122, and aninner circumferential portion of the main body portion 1128 slidablycontacts with the small-outer-diameter portion 1124 of the secondhousing member 1116. That is, the intermediate piston 1110 is disposedsuch that the small-outer-diameter portion 1124 of the second housingmember 1116 is inserted in the main body portion 1128, in other words,such that the main body portion 1128 is interposed between theintermediate portion 1122 of the first housing member 1114 and thesmall-outer-diameter portion 1124 of the second housing member 1116. Soto speak, the intermediate portion 1122 of the first housing member 1114can be considered to be an outer cylindrical portion of the housing1104. In addition, the first pressurizing piston 1106 and theintermediate piston 1110 are disposed such that a front end face of theintermediate piston 1110 abuts on a rear end face of the firstpressurizing piston 1106 in no brake operation.

The input piston 1112 has a roughly a hollow cylindrical shape and isconnected, at a rear end thereof, to the operation rod 72. The inputpiston 1112 is fitted in the second housing member 1116 with seals.Additionally, between a bottom face of the rearward-opening blind holeof the intermediate piston 1110 and a front end face of the input piston1112, two compression coil springs 1132, 1134 each of which generates anelastic reaction force in a direction of separating the intermediatepiston 1110 and the input piston 1112 are disposed in series in thefront-back direction. It is noted that the spring constant of the spring1134 is smaller than the spring constant of the spring 1132.Additionally, between the springs 1132, 1134, a floating seat 1136 isdisposed such that it is supported by them.

In the master cylinder device 1102 constructed thus, between a rear endface of the first pressurizing portion 1106 and a front end face of theintermediate piston 1110, there is defined a fluid chamber R94 intowhich the brake fluid from the high pressure source device 58 isinputted. This fluid chamber R94 is referred to as a “first inputchamber”, where appropriate. Also, between a rear end of the flange 1130of the intermediate piston 1110 and a stepping face formed between thesmall-outer-diameter portion 1124 and the large-outer-diameter portion1126 of the second housing member 1116, there is defined another fluidchamber R95 into which the brake fluid from the high pressure sourcedevice 58 is inputted. This fluid chamber R95 is referred to as a“second input chamber”, where appropriate. It is noted that each of theinput chambers R94, R95 is illustrated in an almost squeezed state inFIG. 13. Additionally, between an inner circumferential face of theintermediate portion 1122 of the first housing member 1114 in front ofthe flange 1130 and an outer circumferential face of the main bodyportion 1128 of the intermediate piston 1110, as described below, thereis defined an annular fluid chamber R96 which opposes the second inputchamber R95 with the flange 1130 being interposed between the fluidchamber R96 and the second input chamber and which can communicate withthe reservoir 62. Hereinafter, this chamber is referred to as an“opposing chamber”, where appropriate. Additionally, in the intermediatepiston 1110, a pressurized area on which a pressure of a brake fluid inthe first input chamber R94 acts, namely, an area of a front end face ofthe front side portion 1128, and a pressurized area on which a pressureof a brake fluid in the second input chamber R95 acts, namely, an areaof a rear end face of the flange 1130 are equal.

In the master cylinder device 1102 in which each of the chambers isdefined thus, the second input chamber R85 is defined by that theintermediate piston 1110 contacts with an inner circumferential face ofthe intermediate portion 1122 of the first housing member 1114 via aseal 1140 embedded in an outer circumferential face of the flange 1130and contacts with an outer circumferential face of thesmall-outer-diameter portion 1124 of the second housing member 1116 viaa seal 1142 embedded in an inner circumferential face of the main bodyportion 1128. By the way, the input piston 1112 slidably contacts withan inner circumferential face of the second housing member 1116, andseals 1144, 1146 are embedded in an inner circumferential face of alarge-outer-diameter portion 1126 of the second housing member 1116. Itis noted that a high-pressure seal is employed as each of the seals1140, 1142 but not employed as each of the seals 1144, 1146.

Between an outer circumferential face of the first pressurizing piston1106 and an inner circumferential face of the small diameter portion ofthe first housing member 1114, there is provided a fluid passage 1160having a certain cross section area through which the brake fluid canflow and connected to the first input chamber R94. In the first housingmember 1114, there is provided a communication hole 1162 whose one endis open to the fluid passage 1160 and whose other end is open to theexterior. That is, the first input chamber R94 communicates with theexterior. Additionally, in the first housing member 1114, there areprovided a communication hole 1164 whose one end is open to the opposingchamber R96 and whose other end is open to the exterior, and acommunication hole 1166 whose one end is open to the second inputchamber R95 and whose other end is open to the exterior. In the secondhousing member 1116, there is provided a communication hole 1168 whoseone end is open to the inter-piston chamber R98. Additionally, in thefirst housing member 1114, there is provided a communication hole 1170whose one end is open so as to face the other end of the communicationhole 1168 and whose other end is open to the exterior. That is, theinter-piston chamber R98 communicates with the exterior. Since an outerdiameter of a part of the second housing member 1116 is slightly smallerthan an inner diameter of the rear large-diameter portion 1120 of thefirst housing member 1114, there is defined a fluid passage 1172 havinga certain cross section area through which the brake fluid can flow. Inthe second housing member 1116, there is provided a communication hole1174 whose one end is open to the fluid passage 1172 and whose other endis open between the seals 1144, 1146 embedded on an innercircumferential face of the second housing member 1116. In the firsthousing member 1112, there is provided a communication hole 1176 whoseone end is open so as to face the other end of the communication hole1174 and whose other end is open to the inter-piston chamber R98. In thefirst housing member 1114, there is provided a communication hole 1178whose one end is open to the fluid passage 1172 and whose other end isopen to the exterior. Accordingly, the inter-piston chamber R98 cancommunicate with the exterior through the fluid passage 1172 and thecommunication holes 1170, 1174, 1176, 1178.

In the master cylinder device 1102 in which the fluid passages and thecommunication holes are formed thus, to the communication hole 1166, aninput pressure passage 230 whose one end is connected to the third fluidchamber 134 of the pressure adjusting valve device 110 is connected atthe other end thereof. Also, an input pressure passage 1180 divergingfrom an input pressure passage 230 is connected to the communicationhole 1162. In addition, an electromagnetic open/close valve 1181 whichis a normally-closed valve is provided on the external communicationpassage 1180. To the communication hole 1164, a low pressure passage1182 communicating with the reservoir 62 is connected, and anelectromagnetic open/close valve 1184 which is a normally-opened valveis provided on the low pressure passage 1182. Therefore, the opposingchamber R96 can communicate with the reservoir 62, thus a mechanismincluding the open/close valve 1184 and the low pressure passage 1182constitutes a low-pressure-source communication mechanism which allowsthe opposing chamber R96 to communicate with the reservoir 62.Additionally, to the communication hole 1170, an external communicationpassage 1186 communicating with the reservoir 62 is connected, and anelectromagnetic open/close valve 1188 which is a normally-closed valveis provided on the external communication passage 1186. Moreover, acommunication passage 1190 diverging from between the end connected tothe communication hole 1170 and the open/close valve 1188 in theexternal communication passage 1186 is connected to the first fluidchamber of the pressure adjusting valve device 100 of thepressure-intensifying/reducing device 60. That is, in the hydraulicbrake system 1100, the pressure adjusting valve device 100 can beactivated by utilizing, as the pilot pressure, not the master pressurebut the pressure of the brake fluid in the inter-piston chamber R98.

<<Actuation of Hydraulic Brake System>>

In the normal condition, since the open/close valve 1181 is opened, thebrake fluid is supplied from the pressure adjusting valve device 100 tothe second input chamber as well as the first input chamber. Asdescribed above, in the intermediate piston 1110, since the pressurizedarea on which the pressure of the brake fluid in the first input chamberR94 acts and the pressurized area on which the pressure of a brake fluidin the second input chamber R95 acts are almost equal, no movement ofthe intermediate piston 1110, or a slight movement if any, occursdepending on the pressures of the brake fluids in the first inputchamber R94 and the second input chamber R95. Additionally, in thenormal condition, since the open/close valve 1184 is closed tohermetically close the opposing chamber R96, a forward movement of theintermediate piston 1110 is prohibited. Moreover, in the normalcondition, the open/close valve 1188 is opened, whereby the inter-pistonchamber R9 communicates with the reservoir 62. Therefore, when a brakeoperation is performed, the input piston 1112 can move forward with thebrake fluid in the inter-piston chamber R98 being flowed into thereservoir 62. Accordingly, in the normal condition, a relative forwardmovement of the input piston 1112 to the intermediate piston 1110 isallowed. By the way, a mechanism including the springs 1132, 1134 servesas a reaction force applying mechanism which applies the operationreaction force to a driver by an increase of the elastic reaction forcedue to the relative forward movement. Additionally, since the springconstants of the springs 1132, 1134 are different from each other asdescribed above, the master cylinder device 1102 is configured suchthat, as the operation amount of the brake pedal 70 increases, a ratioof increase of the operation reaction force increases. On the otherhand, the first pressurizing piston 1106 is moved forward depending onthe pressure of the brake fluid in the first pressurizing piston R94.That is, in the normal condition, a high-pressure-source-pressuredependent pressurizing state in which the brake fluid in thepressurizing chambers R3, R4 can be pressurized depending on only thepressure of the brake fluid in the first input chamber R94 is realized.

In the large-brake-force-required condition, the open/close valve 1184is opened, thereby allowing the forward movement of the intermediatepiston 1110 in the hydraulic brake system 1100. Accordingly, theintermediate piston 1110 can move forward by a force according to thepressure of the brake fluid in the second input chamber R95. Since theintermediate piston 1110 abuts on the first pressurizing piston 1106,the intermediate piston 1110 moves the pressurizing pistons 1006, 1008forward to pressurize the brake fluid to be supplied to the brakedevices 56. In addition, since a forward bias force acts on theintermediate piston 1110 due to the elastic reaction forces by thesprings 1132, 1134, the intermediate piston 1110 is moved by theoperation force as well. That is, the pressurizing pistons 1106, 1108can move forward depending on not only the pressure of the brake fluidin the second input chamber R95 but also the operation force, wherebythe brake fluids in the pressurizing chambers R3, R4 are pressurized.Accordingly, in the master cylinder device 1102, theoperation-force/high-pressure-source-pressure dependent pressurizingstate is realized in the large-brake-force-required condition.Therefore, the intermediate piston 1110 can be considered a pressurereceiving piston which pressurizes the brake fluid to be supplied to thebrake devices 56 by receiving the operation force or the pressure of thebrake fluid supplied to the second input chamber R95.

In the large-brake-force-required condition, the open/close valve 1188is closed. Accordingly, the inter-piston chamber R98 is hermeticallyclosed, the operation force can be transmitted, via the brake fluid inthe inter-piston chamber R98, to the first pressurizing piston 1106.That is, in the master cylinder device 1102, a mechanism including theexternal communication passage 1186 and the open/close valve 1188constitutes an inter-piston-chamber hermetically closing mechanism whichcan hermetically close the inter-piston chamber R98. Also, thisinter-piston-chamber hermetically closing mechanism can be considered asan input-piston-relative-forward-movement prohibiting mechanism whichprohibits a relative forward movement of the input piston 1112 relativeto the intermediate piston 1110. In the large-brake-force-requiredcondition, the open/close valve 1181 is closed to hermetically close thefirst input chamber. Therefore, the brake fluids in the pressurizingchambers R3, R4 can be pressurized while the intermediate piston 1010does not abut on the first pressurizing piston 1006. Therefore, owing tothe closing of the open/close valve 1188 and the closing of theopen/close valve 1181, the brake operation force by the driver istransmitted to the intermediate piston 1110 and the first pressurizingpiston 1106 without generating an ineffective brake operation amount.Incidentally, in the operation-force/high-pressure-source-pressuredependent pressurizing state, since the pressure of the brake fluids inthe pressurizing chambers R3, R4 is transmitted to the input piston1112, the driver can feel the rearward bias force generated by thepressure as the operation reaction force.

In a condition in which electric power is not supplied to the hydraulicbrake system 1100 due to an electric failure, since the open/close valve1184 is de-energized to be opened, the forward movement of theintermediate piston 1010 is allowed as in the large-brake-force-requiredcondition, whereby the pressurizing pistons 1106, 1108 can be movedforward by the operation force. That is, in the master cylinder device1102, it is possible to pressurize the brake fluids in the pressurizingchambers R3, R4 depending on only the operation force so as to supplythe brake fluid to the brake devices 56FL, 56FR. That is, in the mastercylinder device 1102, the operation-force dependent pressurizing stateis realized. Additionally, in an electric failure, the open/close valve1188 is de-energized to be closed, thus the inter-piston chamber R98 ishermetically closed. Therefore, the brake operation force by the driveris transmitted to the pressurizing pistons 1106, 1108 without generatingan ineffective brake operation amount. In addition, in the hydraulicbrake system 1100, when an electric failure etc. occurs, the pressureadjusting valve device 100 can be activated by utilizing the pressure ofthe brake fluid in the inter-piston chamber R98 as the pilot pressure.Therefore, unlike utilizing, as the pilot pressure, the master pressurewhich is affected by a friction force etc. upon a movement of theintermediate piston 1110, the activation of the pressure adjusting valvedevice 100 is comparatively favorable in an ability of following achange of brake operation.

In the master cylinder device 1102, the input piston 1112 is not fittedto the intermediate piston 1110 with any seal. Therefore, even when theintermediate piston 1110 is moved by the pressure of the brake fluid inthe second input chamber R95, no force resulting from any friction forceof any seal acts on the input piston 1112. In addition, each of thehigh-pressure seals 1140, 1142 between the intermediate piston 1110 andthe housing 1104 causes a comparatively large friction force upon amovement of the intermediate piston 1110, whereas each of the seals1144, 1146 between the input piston 1112 and the housing 1104 causes acomparatively small friction force upon a movement of the input piston1112. Therefore, in the master cylinder device 1102, operational feelingin a brake operation is excellent. Especially in the operation-forcedependent pressurizing state, it is possible to provide excellentoperational feeling.

REFERENCE SIGNS LIST

40: hydraulic brake system 50: master cylinder device 56: brake device58: high pressure source device (high pressure source) 60:pressure-intensifying/reducing device (pressure adjusting device) 62:reservoir (low pressure source) 70: brake pedal (brake operation member)90: hydraulic pump 92: accumulator 100: pressure adjusting valve device(pilot-pressure-dependent pressure reducing mechanism) 150: housing 152:first pressurizing piston (pressure receiving piston) 156: input piston164: third housing member (partition portion) 178: through hole(opening) 180: main body portion 182: extension portion 184: flange 234:external communication passage (inter-chamber communication passage,low-pressure-source communication mechanism for the opposing andinter-piston chambers) 238: electromagnetic open/close valve(low-pressure-source communication mechanism for the opposing andinter-piston chambers) 250: reaction force generating device (reactionforce applying mechanism) 256: compression coil spring(elastic-reaction-force applying mechanism for the fluid storagechamber) R1: front side chamber R2: rear side chamber R3: firstpressurizing chamber (pressurizing chamber) R5: input chamber R6:opposing chamber R8: inter-piston chamber R9: fluid storage chamber 300:hydraulic brake system 302: master cylinder device 304: housing 306:first pressurizing piston (pressure receiving piston) 310: input piston316: third housing member (partition portion) 326: through hole(opening) 330: main body portion 332: extension portion 334: flange 342:compression coil spring (elastic-reaction-force applying mechanism forthe input piston) 380: internal communication passage (inter-chambercommunication passage) 382: external communication passage(low-pressure-source communication mechanism for the opposing andinter-piston chambers) 384: electric open/close valve(low-pressure-source communication mechanism for the opposing andinter-piston chambers) 388: external communication passage(input-piston-shrink prohibiting mechanism) 390: electromagneticopen/close valve (input-piston-shrink prohibiting mechanism) R11: frontside chamber R12: rear side chamber R15: input chamber R16: opposingchamber R18: inter-piston chamber 400: hydraulic brake system 402:master cylinder device 404: housing 406: first pressurizing piston(pressure receiving piston) 410: input piston 418: front side portion(partition portion, inner cylindrical portion) 422: intermediate portion(partition portion, separation wall portion) 428: main body portion 430:cylindrical portion 432: flange 440: compression coil spring(elastic-reaction-force applying mechanism for the input piston) 442:compression coil spring (elastic-reaction-force applying mechanism forthe input piston) 460: communication passage (inter-chambercommunication passage) 464: clearance (inter-chamber communicationpassage) R21: front side chamber R22: rear side chamber R25: inputchamber R26: opposing chamber R28: inter-piston chamber 500: hydraulicbrake system 502: master cylinder device 504: housing 506: firstpressurizing piston (pressure receiving piston) 510: input piston 520:inner flange (partition portion) 522: through hole (opening) 526: mainbody portion 528: extension portion 530: flange 544: seal(inter-piston-chamber hermetically closing mechanism) 574: communicationhole (inter-piston-chamber hermetically closing mechanism) 576:communication hole (inter-piston-chamber hermetically closing mechanism)584: external communication passage (inter-chamber communicationpassage, low-pressure-source communication mechanism for the opposingand inter-piston chambers) 586: electromagnetic open/close valve(low-pressure-source communication mechanism for the opposing andinter-piston chambers, inter-piston-chamber hermetically closingmechanism) 588: external communication passage (low-pressure-sourcecommunication mechanism for the opposing and inter-piston chambers) 590:electromagnetic open/close valve (low-pressure-source communicationmechanism for the opposing and inter-piston chambers,low-pressure-source communication mechanism for the opposing chamber)R31: front side chamber R32: rear side chamber R35: input chamber R36:opposing chamber R38: inter-piston chamber 600: hydraulic brake system602: master cylinder device 604: housing 606: first pressurizing piston610: pressure receiving piston 612: input piston 624:small-outer-diameter portion (partition portion, inner cylindricalportion) 626: large-outer-diameter portion (partition portion,separation wall portion) 628: cylindrical portion R41: front sidechamber R42: rear side chamber R45: input chamber R48: inter-pistonchamber 700: hydraulic brake system 702: master cylinder device 704:housing 706: first pressurizing piston (pressure receiving piston) 710:input piston 722: front side portion (partition portion, separation wallportion) 730: main body portion 734: cylindrical portion 736:compression coil spring (reaction force applying mechanism) 738:compression coil spring (reaction force applying mechanism) 744: seal(inter-chamber communication passage) 750: seal (inter-piston-chamberhermetically closing mechanism) 760: communication hole(inter-piston-chamber hermetically closing mechanism) 762: communicationhole (inter-piston-chamber hermetically closing mechanism) 764:communication hole (inter-piston-chamber hermetically closing mechanism)766: communication hole (inter-piston-chamber hermetically closingmechanism) R51: front side chamber R52: rear side chamber R55: inputchamber R57: internal chamber R58: inter-piston chamber 800: hydraulicbrake system 802: master cylinder device 804: housing 806: firstpressurizing piston 810: pressure receiving piston 812: input piston824: inner cylindrical portion (partition portion) 826: front sideportion (main body portion) 830: rear side portion (extension portion)834: compression coil spring (reaction force applying mechanism) 836:compression coil spring (reaction force applying mechanism) 868:external communication passage (inter-chamber communication passage)870: electromagnetic open/close valve (inter-chamber communicationpassage) R61: front side chamber R62: rear side chamber R65: inputchamber R68: inter-piston chamber 900: hydraulic brake system 902:master cylinder device 904: housing 906: first pressurizing piston 910:pressure receiving piston 912: input piston 924: inner cylindricalportion (partition portion) 928: front side portion (main body portion)930: rear side portion (extension portion) 932: flange 934: compressioncoil spring (reaction force applying mechanism) 936: compression coilspring (reaction force applying mechanism) 942: seal(inter-piston-chamber hermetically closing mechanism) 982: externalcommunication passage (low-pressure-source communication mechanism) 984:electromagnetic open/close valve (low-pressure-source communicationmechanism) R71: front side chamber R72: rear side chamber R74: firstinput chamber R75: second input chamber R76: opposing chamber R78:inter-piston chamber 1000: hydraulic brake system 1002: master cylinderdevice 1004: housing 1006: first pressurizing piston 1010: pressurereceiving piston 1012: input piston 1024: small-outer-diameter portion(partition portion, inner cylindrical portion) 1026:large-outer-diameter portion (partition portion, inner cylindricalportion) 1028: main body portion 1030: flange 1038: compression coilspring (reaction force applying mechanism) 1040: compression coil spring(reaction force applying mechanism) 1082: external communication passage(low-pressure-source communication mechanism) 1084: electromagneticopen/close valve (low-pressure-source communication mechanism) 1086:external communication passage (input-piston-relative-forward-movementprohibiting mechanism) 1088: electromagnetic open/close valve(input-piston-relative-forward-movement prohibiting mechanism) R81:front side chamber R82: rear side chamber R84: first input chamber R85:second input chamber R86: opposing chamber R88: inter-piston chamber1100: hydraulic brake system 1102: master cylinder device 1104: housing1106: first pressurizing piston 1110: pressure receiving piston 1112:input piston 1124: small-outer-diameter portion (partition portion,inner cylindrical portion) 1126: large-outer-diameter portion (partitionportion, inner cylindrical portion) 1128: main body portion 1130: flange1132: compression coil spring (reaction force applying mechanism) 1134:compression coil spring (reaction force applying mechanism) 1182:external communication passage (low-pressure-source communicationmechanism) 1184: electromagnetic open/close valve (low-pressure-sourcecommunication mechanism) 1186: external communication passage(inter-piston-chamber hermetically closing mechanism,input-piston-relative-forward-movement prohibiting mechanism) 1088:electromagnetic open/close valve (inter-piston-chamber hermeticallyclosing mechanism, input-piston-relative-forward-movement prohibitingmechanism) R91: front side chamber R92: rear side chamber R94: firstinput chamber R95: second input chamber R96: opposing chamber R98:inter-piston chamber

The invention claimed is:
 1. A master cylinder device for supplying apressurized brake fluid to a brake device provided in a wheel,comprising: a housing whose front side end is closed and which includesa partition portion separating an interior of the housing into a frontside chamber and a rear side chamber and having an opening through thepartition portion; a pressure receiving piston which includes (a) a mainbody portion having a flange on a rear end thereof and disposed in thefront side chamber, and (b) an extension portion extending from the mainbody portion through the opening of the partition portion into the rearside chamber, the pressure receiving piston being moved forward byreceiving a force for pressurizing the brake fluid to be supplied to thebrake device; and an input piston which is disposed in the rear sidechamber, which is connected to a brake operation member disposed behindthe housing, and which can move forward by an operation force applied tothe brake operation member, wherein the main body portion of thepressure receiving piston is fitted, at the flange and a portion infront of the flange, in the housing with respective seals therebetweenand the extension portion of the pressure receiving piston is fitted inthe partition portion of the housing with a seal, whereby: apressurizing chamber in which the brake fluid to be supplied to thebrake device is pressurized by a forward movement of the pressurereceiving piston is defined in front of the main body portion of thepressure receiving piston; an input chamber into which a brake fluidfrom a high pressure source is introduced is defined between a rear endof the main body portion and the partition portion; and an opposingchamber which opposes the input chamber with the flange being interposedbetween the opposing chamber and the input chamber is defined around themain body portion, wherein the input piston is fitted in the housingwith a seal, whereby, between the input piston and the pressurereceiving piston, there is defined an inter-piston chamber such that arear end of the extension portion and the input piston face to eachother in a state in which any seal is not present between the inputpiston and the pressure receiving piston, wherein an inter-chambercommunication passage which allows a communication between the opposingchamber and the inter-piston chamber is provided, and a pressurized areaof the pressure receiving piston on which a pressure of a brake fluid inthe opposing chamber acts and a pressurized area of the pressurereceiving piston on which a pressure of a brake fluid in theinter-piston chamber acts are equal, and wherein the master cylinderdevice further comprises a reaction force applying mechanism whichallows a forward movement of the input piston relative to the housing bythe operation force, and which applies, to the input piston, a reactionforce against the forward movement and with a magnitude according to anamount of the forward movement, as an operation reaction force againstan operation of the brake operation member.
 2. The master cylinderdevice according to claim 1, wherein one of a front side portion of theinput piston and a rear side portion of the extension portion of thepressure receiving piston is formed into a hollow cylindrical shape, andthe other of them is inserted in the one of them.
 3. The master cylinderdevice according to claim 1, wherein the reaction force applyingmechanism includes a fluid storage chamber communicating with theopposing chamber and the inter-piston chamber, and anelastic-reaction-force applying mechanism for the fluid storage chamberwhich allows an increase of a volume of the fluid storage chamberaccording to a decrease of a total volume of the opposing chamber andthe inter-piston chamber, and which applies an elastic reaction forcewith a magnitude according to an amount of the increase of the volume toa brake fluid in the fluid storage chamber.
 4. The master cylinderdevice according to claim 1, wherein the reaction force applyingmechanism includes an elastic-reaction-force applying mechanism for theinput piston which allows a front end portion of the input pistondefining the inter-piston chamber to recede relative to another portionconnected to the brake operation member, thereby allowing the inputpiston to shrink, and which applies an elastic reaction force with amagnitude according to an amount of the shrink of the input piston. 5.The master cylinder device according to claim 1, wherein a front endportion of the input piston defining the inter-piston chamber is allowedto recede relative to another portion connected to the brake operationmember, whereby the input piston is allowed to shrink, and wherein themaster cylinder device further comprises an input-piston-shrinkprohibiting mechanism which prohibits the shrink of the input piston. 6.The master cylinder device according to claim 1, wherein the mastercylinder device comprises a low-pressure-source communication mechanismfor the opposing and inter-piston chambers which allows the opposingchamber and the inter-piston chamber to communicate with a low pressuresource.
 7. The master cylinder device according to claim 1, wherein themaster cylinder device comprises a low-pressure-source communicationmechanism for the opposing chamber which allows the opposing chamber tocommunicate with a low pressure source, and an inter-piston-chamberhermetically closing mechanism which hermetically closes theinter-piston chamber.
 8. A hydraulic brake system, comprising: themaster cylinder device according to claim 1; and a pressure adjustingdevice which adjusts a pressure of a brake fluid to be introduced fromthe high pressure source device to the input chambers of the mastercylinder device.
 9. The hydraulic brake system according to claim 8,wherein the pressure adjusting device is configured to be controlled toreduce the pressure of the brake fluid supplied from the high pressuresource to a pressure according to the control, and configured to supplythe pressure-reduced brake fluid to the master cylinder device, andwherein the pressure adjusting device includes apilot-pressure-dependent pressure reducing mechanism which utilizes, asa pilot pressure, any one of a pressure of the brake fluid in thepressurizing chamber, a pressure of the brake fluid in the opposingchamber, and a pressure of the brake fluid in the inter-piston chamber,and which reduces the pressure of the brake fluid supplied from the highpressure source device to a pressure according to the pilot pressure.10. A master cylinder device for supplying a pressurized brake fluid toa brake device provided in a wheel, comprising: a housing whose frontside end is closed and which includes a partition portion separating aninterior of the housing into a front side chamber and a rear sidechamber and having an opening through the partition portion; a pressurereceiving piston which includes (a) a main body portion having a flangeon a rear end thereof and disposed in the front side chamber and (b) anextension portion extending from the main body portion through theopening of the partition portion into the rear side chamber, thepressure receiving piston being moved forward by receiving a force forpressurizing the brake fluid to be supplied to the brake device; apressurizing piston disposed in the front side chamber and in front ofthe pressure receiving piston; and an input piston which is disposed inthe rear side chamber, which is connected to a brake operation memberdisposed behind the housing, and which is moved forward by an operationforce applied to the brake operation member, wherein the pressurizingpiston is fitted in the housing with a seal, the main body portion ofthe pressure receiving piston is fitted, at the flange and a portion infront of the flange, in the housing with respective seals therebetween,and the extension portion of the pressure receiving piston is fitted inthe partition portion with a seal, whereby: a pressurizing chamber inwhich the brake fluid to be supplied to the brake device is pressurizedby a forward movement of the pressurizing piston is defined in front ofthe pressurizing piston; a first input chamber into which a brake fluidfrom a high pressure source is introduced is defined between the mainbody portion of the pressure receiving piston and the pressurizingpiston; a second input chamber into which the brake fluid from the highpressure source is introduced is defined between a rear end of the mainbody portion of the pressure receiving piston and the partition portion;and an opposing chamber which opposes the second input chamber with theflange being interposed between the opposing and second input chambersis defined around the main body portion of the pressure receivingpiston, wherein the input piston is fitted in the housing with a seal,whereby, between the input piston and the pressure receiving piston,there is defined an inter-piston chamber such that a rear end of theextension portion and the input piston face to each other in a state inwhich any seal is not present between the input piston and the pressurereceiving piston, wherein the master cylinder device is configured suchthat a pressurized area of the pressure receiving piston on which apressure of the brake fluid in the first input chamber acts and apressurized area of the pressure receiving piston on which a pressure ofthe brake fluid in the second input chamber acts are equal, and suchthat, when the respective brake fluids are introduced from the highpressure source into the first input chamber and the second inputchamber with the opposing chamber being hermetically closed, a forwardmovement of the pressure receiving piston is prohibited and the brakefluid in the pressurizing chamber is pressurized by the forward movementof the pressurizing piston, and wherein the master cylinder devicefurther comprises a reaction force applying mechanism which isconfigured to allow a relative forward movement of the input pistonrelative to the pressure receiving piston by the operation force in astate in which a decrease of a volume of the inter-piston chamber isallowed, and which is configured to apply to the pressure receivingpiston and the input piston a reaction force against the relativeforward movement and with a magnitude according to an amount of therelative forward movement such that the reaction force acts as anoperation reaction force against an operation of the brake operationmember.